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Bacteriophage lambda: A temperate inducible phage and type species of the genus lambda-like viruses, in the family SIPHOVIRIDAE. Its natural host is E. coli K12. Its VIRION contains linear double-stranded DNA with single-stranded 12-base 5' sticky ends. The DNA circularizes on infection.Bacteriophages: Viruses whose hosts are bacterial cells.Coliphages: Viruses whose host is Escherichia coli.Lysogeny: The phenomenon by which a temperate phage incorporates itself into the DNA of a bacterial host, establishing a kind of symbiotic relation between PROPHAGE and bacterium which results in the perpetuation of the prophage in all the descendants of the bacterium. Upon induction (VIRUS ACTIVATION) by various agents, such as ultraviolet radiation, the phage is released, which then becomes virulent and lyses the bacterium.Escherichia coli: A species of gram-negative, facultatively anaerobic, rod-shaped bacteria (GRAM-NEGATIVE FACULTATIVELY ANAEROBIC RODS) commonly found in the lower part of the intestine of warm-blooded animals. It is usually nonpathogenic, but some strains are known to produce DIARRHEA and pyogenic infections. Pathogenic strains (virotypes) are classified by their specific pathogenic mechanisms such as toxins (ENTEROTOXIGENIC ESCHERICHIA COLI), etc.DNA, Viral: Deoxyribonucleic acid that makes up the genetic material of viruses.Bacteriophage T4: Virulent bacteriophage and type species of the genus T4-like phages, in the family MYOVIRIDAE. It infects E. coli and is the best known of the T-even phages. Its virion contains linear double-stranded DNA, terminally redundant and circularly permuted.Viral Proteins: Proteins found in any species of virus.Base Sequence: The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.DNA Viruses: Viruses whose nucleic acid is DNA.Bacteriophage T7: Virulent bacteriophage and type species of the genus T7-like phages, in the family PODOVIRIDAE, that infects E. coli. It consists of linear double-stranded DNA, terminally redundant, and non-permuted.Genes, Viral: The functional hereditary units of VIRUSES.T-Phages: A series of 7 virulent phages which infect E. coli. The T-even phages T2, T4; (BACTERIOPHAGE T4), and T6, and the phage T5 are called "autonomously virulent" because they cause cessation of all bacterial metabolism on infection. Phages T1, T3; (BACTERIOPHAGE T3), and T7; (BACTERIOPHAGE T7) are called "dependent virulent" because they depend on continued bacterial metabolism during the lytic cycle. The T-even phages contain 5-hydroxymethylcytosine in place of ordinary cytosine in their DNA.Viral Regulatory and Accessory Proteins: A broad category of viral proteins that play indirect roles in the biological processes and activities of viruses. Included here are proteins that either regulate the expression of viral genes or are involved in modifying host cell functions. Many of the proteins in this category serve multiple functions.Recombination, Genetic: Production of new arrangements of DNA by various mechanisms such as assortment and segregation, CROSSING OVER; GENE CONVERSION; GENETIC TRANSFORMATION; GENETIC CONJUGATION; GENETIC TRANSDUCTION; or mixed infection of viruses.Mutation: Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations.Plasmids: Extrachromosomal, usually CIRCULAR DNA molecules that are self-replicating and transferable from one organism to another. They are found in a variety of bacterial, archaeal, fungal, algal, and plant species. They are used in GENETIC ENGINEERING as CLONING VECTORS.Bacteriophage mu: A temperate coliphage, in the genus Mu-like viruses, family MYOVIRIDAE, composed of a linear, double-stranded molecule of DNA, which is able to insert itself randomly at any point on the host chromosome. It frequently causes a mutation by interrupting the continuity of the bacterial OPERON at the site of insertion.Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.Attachment Sites, Microbiological: Specific loci on both the bacterial DNA (attB) and the phage DNA (attP) which delineate the sites where recombination takes place between them, as the phage DNA becomes integrated (inserted) into the BACTERIAL DNA during LYSOGENY.Genes: A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms.DNA Restriction Enzymes: Enzymes that are part of the restriction-modification systems. They catalyze the endonucleolytic cleavage of DNA sequences which lack the species-specific methylation pattern in the host cell's DNA. Cleavage yields random or specific double-stranded fragments with terminal 5'-phosphates. The function of restriction enzymes is to destroy any foreign DNA that invades the host cell. Most have been studied in bacterial systems, but a few have been found in eukaryotic organisms. They are also used as tools for the systematic dissection and mapping of chromosomes, in the determination of base sequences of DNAs, and have made it possible to splice and recombine genes from one organism into the genome of another. EC 3.21.1.Cloning, Molecular: The insertion of recombinant DNA molecules from prokaryotic and/or eukaryotic sources into a replicating vehicle, such as a plasmid or virus vector, and the introduction of the resultant hybrid molecules into recipient cells without altering the viability of those cells.Bacteriophage phi 6: Virulent bacteriophage and sole member of the genus Cystovirus that infects Pseudomonas species. The virion has a segmented genome consisting of three pieces of doubled-stranded DNA and also a unique lipid-containing envelope.Bacteriolysis: Rupture of bacterial cells due to mechanical force, chemical action, or the lytic growth of BACTERIOPHAGES.Bacteriophage phi X 174: The type species of the genus MICROVIRUS. A prototype of the small virulent DNA coliphages, it is composed of a single strand of supercoiled circular DNA, which on infection, is converted to a double-stranded replicative form by a host enzyme.DNA Replication: The process by which a DNA molecule is duplicated.Integrases: Recombinases that insert exogenous DNA into the host genome. Examples include proteins encoded by the POL GENE of RETROVIRIDAE and also by temperate BACTERIOPHAGES, the best known being BACTERIOPHAGE LAMBDA.Viral Tail Proteins: Proteins found in the tail sections of DNA and RNA viruses. It is believed that these proteins play a role in directing chain folding and assembly of polypeptide chains.Bacteriophage P2: A species of temperate bacteriophage in the genus P2-like viruses, family MYOVIRIDAE, which infects E. coli. It consists of linear double-stranded DNA with 19-base sticky ends.Amino Acid Sequence: The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.DNA-Directed RNA Polymerases: Enzymes that catalyze DNA template-directed extension of the 3'-end of an RNA strand one nucleotide at a time. They can initiate a chain de novo. In eukaryotes, three forms of the enzyme have been distinguished on the basis of sensitivity to alpha-amanitin, and the type of RNA synthesized. (From Enzyme Nomenclature, 1992).DNA, Recombinant: Biologically active DNA which has been formed by the in vitro joining of segments of DNA from different sources. It includes the recombination joint or edge of a heteroduplex region where two recombining DNA molecules are connected.DNA, Bacterial: Deoxyribonucleic acid that makes up the genetic material of bacteria.Bacteriophage M13: Temperate bacteriophage of the genus INOVIRUS which infects enterobacteria, especially E. coli. It is a filamentous phage consisting of single-stranded DNA and is circularly permuted.Operon: In bacteria, a group of metabolically related genes, with a common promoter, whose transcription into a single polycistronic MESSENGER RNA is under the control of an OPERATOR REGION.Bacterial Proteins: Proteins found in any species of bacterium.DNA Nucleotidyltransferases: Enzymes that catalyze the incorporation of deoxyribonucleotides into a chain of DNA. EC 2.7.7.-.Bacteriophage T3: Bacteriophage in the genus T7-like phages, of the family PODOVIRIDAE, which is very closely related to BACTERIOPHAGE T7.Transcription, Genetic: The biosynthesis of RNA carried out on a template of DNA. The biosynthesis of DNA from an RNA template is called REVERSE TRANSCRIPTION.Chromosome Mapping: Any method used for determining the location of and relative distances between genes on a chromosome.Transduction, Genetic: The transfer of bacterial DNA by phages from an infected bacterium to another bacterium. This also refers to the transfer of genes into eukaryotic cells by viruses. This naturally occurring process is routinely employed as a GENE TRANSFER TECHNIQUE.Immunoglobulin lambda-Chains: One of the types of light chain subunits of the immunoglobulins with a molecular weight of approximately 22 kDa.Bacteriophage P1: A species of temperate bacteriophage in the genus P1-like viruses, family MYOVIRIDAE, which infects E. coli. It is the largest of the COLIPHAGES and consists of double-stranded DNA, terminally redundant, and circularly permuted.Bacteriophage Typing: A technique of bacterial typing which differentiates between bacteria or strains of bacteria by their susceptibility to one or more bacteriophages.Integration Host Factors: Bacterial proteins that are used by BACTERIOPHAGES to incorporate their DNA into the DNA of the "host" bacteria. They are DNA-binding proteins that function in genetic recombination as well as in transcriptional and translational regulation.Endodeoxyribonucleases: A group of enzymes catalyzing the endonucleolytic cleavage of DNA. They include members of EC 3.1.21.-, EC 3.1.22.-, EC 3.1.23.- (DNA RESTRICTION ENZYMES), EC 3.1.24.- (DNA RESTRICTION ENZYMES), and EC 3.1.25.-.Salmonella Phages: Viruses whose host is Salmonella. A frequently encountered Salmonella phage is BACTERIOPHAGE P22.Genes, Bacterial: The functional hereditary units of BACTERIA.Prophages: Genomes of temperate BACTERIOPHAGES integrated into the DNA of their bacterial host cell. The prophages can be duplicated for many cell generations until some stimulus induces its activation and virulence.Siphoviridae: A family of BACTERIOPHAGES and ARCHAEAL VIRUSES which are characterized by long, non-contractile tails.Deoxyribonucleases: Enzymes which catalyze the hydrolases of ester bonds within DNA. EC 3.1.-.DNA Packaging: The folding of an organism's DNA molecule into a compact, orderly structure that fits within the limited space of a CELL or VIRUS PARTICLE.Genes, Regulator: Genes which regulate or circumscribe the activity of other genes; specifically, genes which code for PROTEINS or RNAs which have GENE EXPRESSION REGULATION functions.Virus Replication: The process of intracellular viral multiplication, consisting of the synthesis of PROTEINS; NUCLEIC ACIDS; and sometimes LIPIDS, and their assembly into a new infectious particle.Escherichia coli Proteins: Proteins obtained from ESCHERICHIA COLI.Nucleic Acid Conformation: The spatial arrangement of the atoms of a nucleic acid or polynucleotide that results in its characteristic 3-dimensional shape.RNA Phages: Bacteriophages whose genetic material is RNA, which is single-stranded in all except the Pseudomonas phage phi 6 (BACTERIOPHAGE PHI 6). All RNA phages infect their host bacteria via the host's surface pili. Some frequently encountered RNA phages are: BF23, F2, R17, fr, PhiCb5, PhiCb12r, PhiCb8r, PhiCb23r, 7s, PP7, Q beta phage, MS2 phage, and BACTERIOPHAGE PHI 6.Viral Plaque Assay: Method for measuring viral infectivity and multiplication in CULTURED CELLS. Clear lysed areas or plaques develop as the VIRAL PARTICLES are released from the infected cells during incubation. With some VIRUSES, the cells are killed by a cytopathic effect; with others, the infected cells are not killed but can be detected by their hemadsorptive ability. Sometimes the plaque cells contain VIRAL ANTIGENS which can be measured by IMMUNOFLUORESCENCE.Bacteriophage PRD1: Bacteriophage and type species in the genus Tectivirus, family TECTIVIRIDAE. They are specific for Gram-negative bacteria.Chromosomes, Bacterial: Structures within the nucleus of bacterial cells consisting of or containing DNA, which carry genetic information essential to the cell.Nucleic Acid Hybridization: Widely used technique which exploits the ability of complementary sequences in single-stranded DNAs or RNAs to pair with each other to form a double helix. Hybridization can take place between two complimentary DNA sequences, between a single-stranded DNA and a complementary RNA, or between two RNA sequences. The technique is used to detect and isolate specific sequences, measure homology, or define other characteristics of one or both strands. (Kendrew, Encyclopedia of Molecular Biology, 1994, p503)Pseudomonas Phages: Viruses whose host is Pseudomonas. A frequently encountered Pseudomonas phage is BACTERIOPHAGE PHI 6.Restriction Mapping: Use of restriction endonucleases to analyze and generate a physical map of genomes, genes, or other segments of DNA.Genome, Viral: The complete genetic complement contained in a DNA or RNA molecule in a virus.Staphylococcus Phages: Viruses whose host is Staphylococcus.DNA: A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine).Adsorption: The adhesion of gases, liquids, or dissolved solids onto a surface. It includes adsorptive phenomena of bacteria and viruses onto surfaces as well. ABSORPTION into the substance may follow but not necessarily.Bacillus Phages: Viruses whose host is Bacillus. Frequently encountered Bacillus phages include bacteriophage phi 29 and bacteriophage phi 105.Podoviridae: A family of bacteriophages which are characterized by short, non-contractile tails.Kinetics: The rate dynamics in chemical or physical systems.Centrifugation, Density Gradient: Separation of particles according to density by employing a gradient of varying densities. At equilibrium each particle settles in the gradient at a point equal to its density. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Binding Sites: The parts of a macromolecule that directly participate in its specific combination with another molecule.Genetics, Microbial: A subdiscipline of genetics which deals with the genetic mechanisms and processes of microorganisms.Streptococcus Phages: Viruses whose host is Streptococcus.Genetic Complementation Test: A test used to determine whether or not complementation (compensation in the form of dominance) will occur in a cell with a given mutant phenotype when another mutant genome, encoding the same mutant phenotype, is introduced into that cell.Operator Regions, Genetic: The regulatory elements of an OPERON to which activators or repressors bind thereby effecting the transcription of GENES in the operon.Suppression, Genetic: Mutation process that restores the wild-type PHENOTYPE in an organism possessing a mutationally altered GENOTYPE. The second "suppressor" mutation may be on a different gene, on the same gene but located at a distance from the site of the primary mutation, or in extrachromosomal genes (EXTRACHROMOSOMAL INHERITANCE).DNA, Single-Stranded: A single chain of deoxyribonucleotides that occurs in some bacteria and viruses. It usually exists as a covalently closed circle.Exonucleases: Enzymes that catalyze the release of mononucleotides by the hydrolysis of the terminal bond of deoxyribonucleotide or ribonucleotide chains.Rho Factor: A protein which effects termination of RNA synthesis during the genetic transcription process by dissociating the ternary transcription complex RNA;-RNA POLYMERASE DNA at the termination of a gene.Temperature: The property of objects that determines the direction of heat flow when they are placed in direct thermal contact. The temperature is the energy of microscopic motions (vibrational and translational) of the particles of atoms.Microscopy, Electron: Microscopy using an electron beam, instead of light, to visualize the sample, thereby allowing much greater magnification. The interactions of ELECTRONS with specimens are used to provide information about the fine structure of that specimen. In TRANSMISSION ELECTRON MICROSCOPY the reactions of the electrons that are transmitted through the specimen are imaged. In SCANNING ELECTRON MICROSCOPY an electron beam falls at a non-normal angle on the specimen and the image is derived from the reactions occurring above the plane of the specimen.Molecular Weight: The sum of the weight of all the atoms in a molecule.Repressor Proteins: Proteins which maintain the transcriptional quiescence of specific GENES or OPERONS. Classical repressor proteins are DNA-binding proteins that are normally bound to the OPERATOR REGION of an operon, or the ENHANCER SEQUENCES of a gene until a signal occurs that causes their release.DNA, Circular: Any of the covalently closed DNA molecules found in bacteria, many viruses, mitochondria, plastids, and plasmids. Small, polydisperse circular DNA's have also been observed in a number of eukaryotic organisms and are suggested to have homology with chromosomal DNA and the capacity to be inserted into, and excised from, chromosomal DNA. It is a fragment of DNA formed by a process of looping out and deletion, containing a constant region of the mu heavy chain and the 3'-part of the mu switch region. Circular DNA is a normal product of rearrangement among gene segments encoding the variable regions of immunoglobulin light and heavy chains, as well as the T-cell receptor. (Riger et al., Glossary of Genetics, 5th ed & Segen, Dictionary of Modern Medicine, 1992)Endonucleases: Enzymes that catalyze the hydrolysis of the internal bonds and thereby the formation of polynucleotides or oligonucleotides from ribo- or deoxyribonucleotide chains. EC 3.1.-.DNA-Binding Proteins: Proteins which bind to DNA. The family includes proteins which bind to both double- and single-stranded DNA and also includes specific DNA binding proteins in serum which can be used as markers for malignant diseases.Levivirus: A bacteriophage genus of the family LEVIVIRIDAE, whose viruses contain the short version of the genome and have a separate gene for cell lysis.Terminator Regions, Genetic: DNA sequences recognized as signals to end GENETIC TRANSCRIPTION.Gene Expression Regulation, Viral: Any of the processes by which cytoplasmic factors influence the differential control of gene action in viruses.Rec A Recombinases: A family of recombinases initially identified in BACTERIA. They catalyze the ATP-driven exchange of DNA strands in GENETIC RECOMBINATION. The product of the reaction consists of a duplex and a displaced single-stranded loop, which has the shape of the letter D and is therefore called a D-loop structure.Ultraviolet Rays: That portion of the electromagnetic spectrum immediately below the visible range and extending into the x-ray frequencies. The longer wavelengths (near-UV or biotic or vital rays) are necessary for the endogenous synthesis of vitamin D and are also called antirachitic rays; the shorter, ionizing wavelengths (far-UV or abiotic or extravital rays) are viricidal, bactericidal, mutagenic, and carcinogenic and are used as disinfectants.Polynucleotide Ligases: Catalyze the joining of preformed ribonucleotides or deoxyribonucleotides in phosphodiester linkage during genetic processes. EC 6.5.1.DNA, Superhelical: Circular duplex DNA isolated from viruses, bacteria and mitochondria in supercoiled or supertwisted form. This superhelical DNA is endowed with free energy. During transcription, the magnitude of RNA initiation is proportional to the DNA superhelicity.RNA, Viral: Ribonucleic acid that makes up the genetic material of viruses.Receptors, Virus: Specific molecular components of the cell capable of recognizing and interacting with a virus, and which, after binding it, are capable of generating some signal that initiates the chain of events leading to the biological response.Promoter Regions, Genetic: DNA sequences which are recognized (directly or indirectly) and bound by a DNA-dependent RNA polymerase during the initiation of transcription. Highly conserved sequences within the promoter include the Pribnow box in bacteria and the TATA BOX in eukaryotes.Capsid: The outer protein protective shell of a virus, which protects the viral nucleic acid.Templates, Genetic: Macromolecular molds for the synthesis of complementary macromolecules, as in DNA REPLICATION; GENETIC TRANSCRIPTION of DNA to RNA, and GENETIC TRANSLATION of RNA into POLYPEPTIDES.Electrophoresis, Polyacrylamide Gel: Electrophoresis in which a polyacrylamide gel is used as the diffusion medium.Chloramphenicol: An antibiotic first isolated from cultures of Streptomyces venequelae in 1947 but now produced synthetically. It has a relatively simple structure and was the first broad-spectrum antibiotic to be discovered. It acts by interfering with bacterial protein synthesis and is mainly bacteriostatic. (From Martindale, The Extra Pharmacopoeia, 29th ed, p106)Nucleic Acid Heteroduplexes: Double-stranded nucleic acid molecules (DNA-DNA or DNA-RNA) which contain regions of nucleotide mismatches (non-complementary). In vivo, these heteroduplexes can result from mutation or genetic recombination; in vitro, they are formed by nucleic acid hybridization. Electron microscopic analysis of the resulting heteroduplexes facilitates the mapping of regions of base sequence homology of nucleic acids.Bacillus subtilis: A species of gram-positive bacteria that is a common soil and water saprophyte.Sequence Homology, Nucleic Acid: The sequential correspondence of nucleotides in one nucleic acid molecule with those of another nucleic acid molecule. Sequence homology is an indication of the genetic relatedness of different organisms and gene function.DNA Transposable Elements: Discrete segments of DNA which can excise and reintegrate to another site in the genome. Most are inactive, i.e., have not been found to exist outside the integrated state. DNA transposable elements include bacterial IS (insertion sequence) elements, Tn elements, the maize controlling elements Ac and Ds, Drosophila P, gypsy, and pogo elements, the human Tigger elements and the Tc and mariner elements which are found throughout the animal kingdom.Nucleic Acid Denaturation: Disruption of the secondary structure of nucleic acids by heat, extreme pH or chemical treatment. Double strand DNA is "melted" by dissociation of the non-covalent hydrogen bonds and hydrophobic interactions. Denatured DNA appears to be a single-stranded flexible structure. The effects of denaturation on RNA are similar though less pronounced and largely reversible.Capsid Proteins: Proteins that form the CAPSID of VIRUSES.TritiumGenetic Code: The meaning ascribed to the BASE SEQUENCE with respect to how it is translated into AMINO ACID SEQUENCE. The start, stop, and order of amino acids of a protein is specified by consecutive triplets of nucleotides called codons (CODON).Inovirus: A genus of filamentous bacteriophages of the family INOVIRIDAE. Organisms of this genus infect enterobacteria, PSEUDOMONAS; VIBRIO; and XANTHOMONAS.Protein Biosynthesis: The biosynthesis of PEPTIDES and PROTEINS on RIBOSOMES, directed by MESSENGER RNA, via TRANSFER RNA that is charged with standard proteinogenic AMINO ACIDS.ThymineGenetic Vectors: DNA molecules capable of autonomous replication within a host cell and into which other DNA sequences can be inserted and thus amplified. Many are derived from PLASMIDS; BACTERIOPHAGES; or VIRUSES. They are used for transporting foreign genes into recipient cells. Genetic vectors possess a functional replicator site and contain GENETIC MARKERS to facilitate their selective recognition.Electrophoresis, Agar Gel: Electrophoresis in which agar or agarose gel is used as the diffusion medium.Protein Binding: The process in which substances, either endogenous or exogenous, bind to proteins, peptides, enzymes, protein precursors, or allied compounds. Specific protein-binding measures are often used as assays in diagnostic assessments.Exodeoxyribonuclease V: An ATP-dependent exodeoxyribonuclease that cleaves in either the 5'- to 3'- or the 3'- to 5'-direction to yield 5'-phosphooligonucleotides. It is primarily found in BACTERIA.Species Specificity: The restriction of a characteristic behavior, anatomical structure or physical system, such as immune response; metabolic response, or gene or gene variant to the members of one species. It refers to that property which differentiates one species from another but it is also used for phylogenetic levels higher or lower than the species.Models, Molecular: Models used experimentally or theoretically to study molecular shape, electronic properties, or interactions; includes analogous molecules, computer-generated graphics, and mechanical structures.Transcription Factors: Endogenous substances, usually proteins, which are effective in the initiation, stimulation, or termination of the genetic transcription process.Virus Assembly: The assembly of VIRAL STRUCTURAL PROTEINS and nucleic acid (VIRAL DNA or VIRAL RNA) to form a VIRUS PARTICLE.DNA Helicases: Proteins that catalyze the unwinding of duplex DNA during replication by binding cooperatively to single-stranded regions of DNA or to short regions of duplex DNA that are undergoing transient opening. In addition DNA helicases are DNA-dependent ATPases that harness the free energy of ATP hydrolysis to translocate DNA strands.Viral Structural Proteins: Viral proteins that are components of the mature assembled VIRUS PARTICLES. They may include nucleocapsid core proteins (gag proteins), enzymes packaged within the virus particle (pol proteins), and membrane components (env proteins). These do not include the proteins encoded in the VIRAL GENOME that are produced in infected cells but which are not packaged in the mature virus particle,i.e. the so called non-structural proteins (VIRAL NONSTRUCTURAL PROTEINS).PolynucleotidesSequence Analysis, DNA: A multistage process that includes cloning, physical mapping, subcloning, determination of the DNA SEQUENCE, and information analysis.Bacteriophage P22: A species of temperate bacteriophage in the genus P22-like viruses, family PODOVIRIDAE, that infects SALMONELLA species. The genome consists of double-stranded DNA, terminally redundant, and circularly permuted.Adenosine Triphosphatases: A group of enzymes which catalyze the hydrolysis of ATP. The hydrolysis reaction is usually coupled with another function such as transporting Ca(2+) across a membrane. These enzymes may be dependent on Ca(2+), Mg(2+), anions, H+, or DNA.Extrachromosomal Inheritance: Vertical transmission of hereditary characters by DNA from cytoplasmic organelles such as MITOCHONDRIA; CHLOROPLASTS; and PLASTIDS, or from PLASMIDS or viral episomal DNA.Protein Conformation: The characteristic 3-dimensional shape of a protein, including the secondary, supersecondary (motifs), tertiary (domains) and quaternary structure of the peptide chain. PROTEIN STRUCTURE, QUATERNARY describes the conformation assumed by multimeric proteins (aggregates of more than one polypeptide chain).Viral Interference: A phenomenon in which infection by a first virus results in resistance of cells or tissues to infection by a second, unrelated virus.Crosses, Genetic: Deliberate breeding of two different individuals that results in offspring that carry part of the genetic material of each parent. The parent organisms must be genetically compatible and may be from different varieties or closely related species.Models, Genetic: Theoretical representations that simulate the behavior or activity of genetic processes or phenomena. They include the use of mathematical equations, computers, and other electronic equipment.Recombinases: A broad category of enzymes that are involved in the process of GENETIC RECOMBINATION.Virus Activation: The mechanism by which latent viruses, such as genetically transmitted tumor viruses (PROVIRUSES) or PROPHAGES of lysogenic bacteria, are induced to replicate and then released as infectious viruses. It may be effected by various endogenous and exogenous stimuli, including B-cell LIPOPOLYSACCHARIDES, glucocorticoid hormones, halogenated pyrimidines, IONIZING RADIATION, ultraviolet light, and superinfecting viruses.Immunoglobulin Light Chains: Polypeptide chains, consisting of 211 to 217 amino acid residues and having a molecular weight of approximately 22 kDa. There are two major types of light chains, kappa and lambda. Two Ig light chains and two Ig heavy chains (IMMUNOGLOBULIN HEAVY CHAINS) make one immunoglobulin molecule.Blotting, Southern: A method (first developed by E.M. Southern) for detection of DNA that has been electrophoretically separated and immobilized by blotting on nitrocellulose or other type of paper or nylon membrane followed by hybridization with labeled NUCLEIC ACID PROBES.Genetic Engineering: Directed modification of the gene complement of a living organism by such techniques as altering the DNA, substituting genetic material by means of a virus, transplanting whole nuclei, transplanting cell hybrids, etc.Porins: Porins are protein molecules that were originally found in the outer membrane of GRAM-NEGATIVE BACTERIA and that form multi-meric channels for the passive DIFFUSION of WATER; IONS; or other small molecules. Porins are present in bacterial CELL WALLS, as well as in plant, fungal, mammalian and other vertebrate CELL MEMBRANES and MITOCHONDRIAL MEMBRANES.Maltose: A dextrodisaccharide from malt and starch. It is used as a sweetening agent and fermentable intermediate in brewing. (Grant & Hackh's Chemical Dictionary, 5th ed)ATP-Dependent Proteases: Proteases that contain proteolytic core domains and ATPase-containing regulatory domains. They are usually comprised of large multi-subunit assemblies. The domains can occur within a single peptide chain or on distinct subunits.Mutagenesis: Process of generating a genetic MUTATION. It may occur spontaneously or be induced by MUTAGENS.Substrate Specificity: A characteristic feature of enzyme activity in relation to the kind of substrate on which the enzyme or catalytic molecule reacts.RNA, Messenger: RNA sequences that serve as templates for protein synthesis. Bacterial mRNAs are generally primary transcripts in that they do not require post-transcriptional processing. Eukaryotic mRNA is synthesized in the nucleus and must be exported to the cytoplasm for translation. Most eukaryotic mRNAs have a sequence of polyadenylic acid at the 3' end, referred to as the poly(A) tail. The function of this tail is not known for certain, but it may play a role in the export of mature mRNA from the nucleus as well as in helping stabilize some mRNA molecules by retarding their degradation in the cytoplasm.Phenotype: The outward appearance of the individual. It is the product of interactions between genes, and between the GENOTYPE and the environment.Base Composition: The relative amounts of the PURINES and PYRIMIDINES in a nucleic acid.Phosphorus Isotopes: Stable phosphorus atoms that have the same atomic number as the element phosphorus, but differ in atomic weight. P-31 is a stable phosphorus isotope.RNA, Bacterial: Ribonucleic acid in bacteria having regulatory and catalytic roles as well as involvement in protein synthesis.Hot Temperature: Presence of warmth or heat or a temperature notably higher than an accustomed norm.Cystoviridae: A family of bacteriophages containing one genus (Cystovirus) with one member (BACTERIOPHAGE PHI 6).Galactokinase: An enzyme that catalyzes reversibly the formation of galactose 1-phosphate and ADP from ATP and D-galactose. Galactosamine can also act as the acceptor. A deficiency of this enzyme results in GALACTOSEMIA. EC 2.7.1.6.Bacterial Outer Membrane Proteins: Proteins isolated from the outer membrane of Gram-negative bacteria.Oligonucleotides: Polymers made up of a few (2-20) nucleotides. In molecular genetics, they refer to a short sequence synthesized to match a region where a mutation is known to occur, and then used as a probe (OLIGONUCLEOTIDE PROBES). (Dorland, 28th ed)Virus Integration: Insertion of viral DNA into host-cell DNA. This includes integration of phage DNA into bacterial DNA; (LYSOGENY); to form a PROPHAGE or integration of retroviral DNA into cellular DNA to form a PROVIRUS.Exodeoxyribonucleases: A family of enzymes that catalyze the exonucleolytic cleavage of DNA. It includes members of the class EC 3.1.11 that produce 5'-phosphomonoesters as cleavage products.Lac Operon: The genetic unit consisting of three structural genes, an operator and a regulatory gene. The regulatory gene controls the synthesis of the three structural genes: BETA-GALACTOSIDASE and beta-galactoside permease (involved with the metabolism of lactose), and beta-thiogalactoside acetyltransferase.Cell-Free System: A fractionated cell extract that maintains a biological function. A subcellular fraction isolated by ultracentrifugation or other separation techniques must first be isolated so that a process can be studied free from all of the complex side reactions that occur in a cell. The cell-free system is therefore widely used in cell biology. (From Alberts et al., Molecular Biology of the Cell, 2d ed, p166)Bacteriophage Pf1: A species of filamentous Pseudomonas phage in the genus INOVIRUS, family INOVIRIDAE.Caudovirales: An order comprising three families of tailed bacteriophages: MYOVIRIDAE; PODOVIRIDAE; and SIPHOVIRIDAE.R Factors: A class of plasmids that transfer antibiotic resistance from one bacterium to another by conjugation.Mutagenesis, Site-Directed: Genetically engineered MUTAGENESIS at a specific site in the DNA molecule that introduces a base substitution, or an insertion or deletion.Conjugation, Genetic: A parasexual process in BACTERIA; ALGAE; FUNGI; and ciliate EUKARYOTA for achieving exchange of chromosome material during fusion of two cells. In bacteria, this is a uni-directional transfer of genetic material; in protozoa it is a bi-directional exchange. In algae and fungi, it is a form of sexual reproduction, with the union of male and female gametes.Recombinant Proteins: Proteins prepared by recombinant DNA technology.DNA-Directed DNA Polymerase: DNA-dependent DNA polymerases found in bacteria, animal and plant cells. During the replication process, these enzymes catalyze the addition of deoxyribonucleotide residues to the end of a DNA strand in the presence of DNA as template-primer. They also possess exonuclease activity and therefore function in DNA repair.SOS Response (Genetics): An error-prone mechanism or set of functions for repairing damaged microbial DNA. SOS functions (a concept reputedly derived from the SOS of the international distress signal) are involved in DNA repair and mutagenesis, in cell division inhibition, in recovery of normal physiological conditions after DNA repair, and possibly in cell death when DNA damage is extensive.Peptide Elongation Factors: Protein factors uniquely required during the elongation phase of protein synthesis.beta-Galactosidase: A group of enzymes that catalyzes the hydrolysis of terminal, non-reducing beta-D-galactose residues in beta-galactosides. Deficiency of beta-Galactosidase A1 may cause GANGLIOSIDOSIS, GM1.Gene Expression Regulation: Any of the processes by which nuclear, cytoplasmic, or intercellular factors influence the differential control (induction or repression) of gene action at the level of transcription or translation.Recombinant Fusion Proteins: Recombinant proteins produced by the GENETIC TRANSLATION of fused genes formed by the combination of NUCLEIC ACID REGULATORY SEQUENCES of one or more genes with the protein coding sequences of one or more genes.Sequence Homology, Amino Acid: The degree of similarity between sequences of amino acids. This information is useful for the analyzing genetic relatedness of proteins and species.Protein Structure, Tertiary: The level of protein structure in which combinations of secondary protein structures (alpha helices, beta sheets, loop regions, and motifs) pack together to form folded shapes called domains. Disulfide bridges between cysteines in two different parts of the polypeptide chain along with other interactions between the chains play a role in the formation and stabilization of tertiary structure. Small proteins usually consist of only one domain but larger proteins may contain a number of domains connected by segments of polypeptide chain which lack regular secondary structure.Peptide Library: A collection of cloned peptides, or chemically synthesized peptides, frequently consisting of all possible combinations of amino acids making up an n-amino acid peptide.Sequence Alignment: The arrangement of two or more amino acid or base sequences from an organism or organisms in such a way as to align areas of the sequences sharing common properties. The degree of relatedness or homology between the sequences is predicted computationally or statistically based on weights assigned to the elements aligned between the sequences. This in turn can serve as a potential indicator of the genetic relatedness between the organisms.Macromolecular Substances: Compounds and molecular complexes that consist of very large numbers of atoms and are generally over 500 kDa in size. In biological systems macromolecular substances usually can be visualized using ELECTRON MICROSCOPY and are distinguished from ORGANELLES by the lack of a membrane structure.Genotype: The genetic constitution of the individual, comprising the ALLELES present at each GENETIC LOCUS.Immunoglobulin kappa-Chains: One of the types of light chains of the immunoglobulins with a molecular weight of approximately 22 kDa.Crossing Over, Genetic: The reciprocal exchange of segments at corresponding positions along pairs of homologous CHROMOSOMES by symmetrical breakage and crosswise rejoining forming cross-over sites (HOLLIDAY JUNCTIONS) that are resolved during CHROMOSOME SEGREGATION. Crossing-over typically occurs during MEIOSIS but it may also occur in the absence of meiosis, for example, with bacterial chromosomes, organelle chromosomes, or somatic cell nuclear chromosomes.Chromosome Deletion: Actual loss of portion of a chromosome.DNA Primase: A single-stranded DNA-dependent RNA polymerase that functions to initiate, or prime, DNA synthesis by synthesizing oligoribonucleotide primers. EC 2.7.7.-.DNA Repair: The reconstruction of a continuous two-stranded DNA molecule without mismatch from a molecule which contained damaged regions. The major repair mechanisms are excision repair, in which defective regions in one strand are excised and resynthesized using the complementary base pairing information in the intact strand; photoreactivation repair, in which the lethal and mutagenic effects of ultraviolet light are eliminated; and post-replication repair, in which the primary lesions are not repaired, but the gaps in one daughter duplex are filled in by incorporation of portions of the other (undamaged) daughter duplex. Excision repair and post-replication repair are sometimes referred to as "dark repair" because they do not require light.Nucleoproteins: Proteins conjugated with nucleic acids.Transformation, Bacterial: The heritable modification of the properties of a competent bacterium by naked DNA from another source. The uptake of naked DNA is a naturally occuring phenomenon in some bacteria. It is often used as a GENE TRANSFER TECHNIQUE.Chromatography: Techniques used to separate mixtures of substances based on differences in the relative affinities of the substances for mobile and stationary phases. A mobile phase (fluid or gas) passes through a column containing a stationary phase of porous solid or liquid coated on a solid support. Usage is both analytical for small amounts and preparative for bulk amounts.Cryoelectron Microscopy: Electron microscopy involving rapid freezing of the samples. The imaging of frozen-hydrated molecules and organelles permits the best possible resolution closest to the living state, free of chemical fixatives or stains.Drug Resistance, Microbial: The ability of microorganisms, especially bacteria, to resist or to become tolerant to chemotherapeutic agents, antimicrobial agents, or antibiotics. This resistance may be acquired through gene mutation or foreign DNA in transmissible plasmids (R FACTORS).Heat-Shock Proteins: Proteins which are synthesized in eukaryotic organisms and bacteria in response to hyperthermia and other environmental stresses. They increase thermal tolerance and perform functions essential to cell survival under these conditions.Oligodeoxyribonucleotides: A group of deoxyribonucleotides (up to 12) in which the phosphate residues of each deoxyribonucleotide act as bridges in forming diester linkages between the deoxyribose moieties.Gene Library: A large collection of DNA fragments cloned (CLONING, MOLECULAR) from a given organism, tissue, organ, or cell type. It may contain complete genomic sequences (GENOMIC LIBRARY) or complementary DNA sequences, the latter being formed from messenger RNA and lacking intron sequences.Hydrolysis: The process of cleaving a chemical compound by the addition of a molecule of water.Galactosidases: A family of galactoside hydrolases that hydrolyze compounds with an O-galactosyl linkage. EC 3.2.1.-.Mitomycins: A group of methylazirinopyrroloindolediones obtained from certain Streptomyces strains. They are very toxic antibiotics used as ANTINEOPLASTIC AGENTS in some solid tumors. PORFIROMYCIN and MITOMYCIN are the most useful members of the group.Structure-Activity Relationship: The relationship between the chemical structure of a compound and its biological or pharmacological activity. Compounds are often classed together because they have structural characteristics in common including shape, size, stereochemical arrangement, and distribution of functional groups.Open Reading Frames: A sequence of successive nucleotide triplets that are read as CODONS specifying AMINO ACIDS and begin with an INITIATOR CODON and end with a stop codon (CODON, TERMINATOR).Biological Therapy: Treatment of diseases with biological materials or biological response modifiers, such as the use of GENES; CELLS; TISSUES; organs; SERUM; VACCINES; and humoral agents.Chromatography, DEAE-Cellulose: A type of ion exchange chromatography using diethylaminoethyl cellulose (DEAE-CELLULOSE) as a positively charged resin. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)HSP40 Heat-Shock Proteins: A family of heat-shock proteins that contain a 70 amino-acid consensus sequence known as the J domain. The J domain of HSP40 heat shock proteins interacts with HSP70 HEAT-SHOCK PROTEINS. HSP40 heat-shock proteins play a role in regulating the ADENOSINE TRIPHOSPHATASES activity of HSP70 heat-shock proteins.Host Specificity: The properties of a pathogen that makes it capable of infecting one or more specific hosts. The pathogen can include PARASITES as well as VIRUSES; BACTERIA; FUNGI; or PLANTS.Codon: A set of three nucleotides in a protein coding sequence that specifies individual amino acids or a termination signal (CODON, TERMINATOR). Most codons are universal, but some organisms do not produce the transfer RNAs (RNA, TRANSFER) complementary to all codons. These codons are referred to as unassigned codons (CODONS, NONSENSE).Culture Media: Any liquid or solid preparation made specifically for the growth, storage, or transport of microorganisms or other types of cells. The variety of media that exist allow for the culturing of specific microorganisms and cell types, such as differential media, selective media, test media, and defined media. Solid media consist of liquid media that have been solidified with an agent such as AGAR or GELATIN.Sewage: Refuse liquid or waste matter carried off by sewers.Genes, Lethal: Genes whose loss of function or gain of function MUTATION leads to the death of the carrier prior to maturity. They may be essential genes (GENES, ESSENTIAL) required for viability, or genes which cause a block of function of an essential gene at a time when the essential gene function is required for viability.Oligonucleotide Probes: Synthetic or natural oligonucleotides used in hybridization studies in order to identify and study specific nucleic acid fragments, e.g., DNA segments near or within a specific gene locus or gene. The probe hybridizes with a specific mRNA, if present. Conventional techniques used for testing for the hybridization product include dot blot assays, Southern blot assays, and DNA:RNA hybrid-specific antibody tests. Conventional labels for the probe include the radioisotope labels 32P and 125I and the chemical label biotin.