Virion: The infective system of a virus, composed of the viral genome, a protein core, and a protein coat called a capsid, which may be naked or enclosed in a lipoprotein envelope called the peplos.Viral Proteins: Proteins found in any species of virus.Virus Assembly: The assembly of VIRAL STRUCTURAL PROTEINS and nucleic acid (VIRAL DNA or VIRAL RNA) to form a VIRUS PARTICLE.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.Capsid: The outer protein protective shell of a virus, which protects the viral nucleic acid.RNA, Viral: Ribonucleic acid that makes up the genetic material of viruses.Cell Line: Established cell cultures that have the potential to propagate indefinitely.Capsid Proteins: Proteins that form the CAPSID of VIRUSES.Viral Envelope Proteins: Layers of protein which surround the capsid in animal viruses with tubular nucleocapsids. The envelope consists of an inner layer of lipids and virus specified proteins also called membrane or matrix proteins. The outer layer consists of one or more types of morphological subunits called peplomers which project from the viral envelope; this layer always consists of glycoproteins.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).DNA, Viral: Deoxyribonucleic acid that makes up the genetic material of viruses.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.Virus Release: Release of a virus from the host cell following VIRUS ASSEMBLY and maturation. Egress can occur by host cell lysis, EXOCYTOSIS, or budding through the plasma membrane.Genes, Viral: The functional hereditary units of VIRUSES.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.Genome, Viral: The complete genetic complement contained in a DNA or RNA molecule in a virus.HIV-1: The type species of LENTIVIRUS and the etiologic agent of AIDS. It is characterized by its cytopathic effect and affinity for the T4-lymphocyte.Cercopithecus aethiops: A species of CERCOPITHECUS containing three subspecies: C. tantalus, C. pygerythrus, and C. sabeus. They are found in the forests and savannah of Africa. The African green monkey (C. pygerythrus) is the natural host of SIMIAN IMMUNODEFICIENCY VIRUS and is used in AIDS research.Vaccinia virus: The type species of ORTHOPOXVIRUS, related to COWPOX VIRUS, but whose true origin is unknown. It has been used as a live vaccine against SMALLPOX. It is also used as a vector for inserting foreign DNA into animals. Rabbitpox virus is a subspecies of VACCINIA VIRUS.Vero Cells: A CELL LINE derived from the kidney of the African green (vervet) monkey, (CERCOPITHECUS AETHIOPS) used primarily in virus replication studies and plaque assays.Gene Products, gag: Proteins coded by the retroviral gag gene. The products are usually synthesized as protein precursors or POLYPROTEINS, which are then cleaved by viral proteases to yield the final products. Many of the final products are associated with the nucleoprotein core of the virion. gag is short for group-specific antigen.Base Sequence: The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.Nucleocapsid: A protein-nucleic acid complex which forms part or all of a virion. It consists of a CAPSID plus enclosed nucleic acid. Depending on the virus, the nucleocapsid may correspond to a naked core or be surrounded by a membranous envelope.Herpesvirus 1, Human: The type species of SIMPLEXVIRUS causing most forms of non-genital herpes simplex in humans. Primary infection occurs mainly in infants and young children and then the virus becomes latent in the dorsal root ganglion. It then is periodically reactivated throughout life causing mostly benign conditions.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.Gene Expression Regulation, Viral: Any of the processes by which cytoplasmic factors influence the differential control of gene action in viruses.Herpesvirus 1, Suid: A species of VARICELLOVIRUS producing a respiratory infection (PSEUDORABIES) in swine, its natural host. It also produces an usually fatal ENCEPHALOMYELITIS in cattle, sheep, dogs, cats, foxes, and mink.Virus Internalization: The entering of cells by viruses following VIRUS ATTACHMENT. This is achieved by ENDOCYTOSIS, by direct MEMBRANE FUSION of the viral membrane with the CELL MEMBRANE, or by translocation of the whole virus across the cell membrane.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.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.Viral Matrix Proteins: Proteins associated with the inner surface of the lipid bilayer of the viral envelope. These proteins have been implicated in control of viral transcription and may possibly serve as the "glue" that binds the nucleocapsid to the appropriate membrane site during viral budding from the host cell.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.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)Ribonucleases: Enzymes that catalyze the hydrolysis of ester bonds within RNA. EC 3.1.-.HeLa Cells: The first continuously cultured human malignant CELL LINE, derived from the cervical carcinoma of Henrietta Lacks. These cells are used for VIRUS CULTIVATION and antitumor drug screening assays.Neutralization Tests: The measurement of infection-blocking titer of ANTISERA by testing a series of dilutions for a given virus-antiserum interaction end-point, which is generally the dilution at which tissue cultures inoculated with the serum-virus mixtures demonstrate cytopathology (CPE) or the dilution at which 50% of test animals injected with serum-virus mixtures show infectivity (ID50) or die (LD50).Antigens, Viral: Substances elaborated by viruses that have antigenic activity.Viral Core Proteins: Proteins found mainly in icosahedral DNA and RNA viruses. They consist of proteins directly associated with the nucleic acid inside the NUCLEOCAPSID.gag Gene Products, Human Immunodeficiency Virus: Proteins encoded by the GAG GENE of the HUMAN IMMUNODEFICIENCY VIRUS.Antibodies, Viral: Immunoglobulins produced in response to VIRAL ANTIGENS.Simplexvirus: A genus of the family HERPESVIRIDAE, subfamily ALPHAHERPESVIRINAE, consisting of herpes simplex-like viruses. The type species is HERPESVIRUS 1, HUMAN.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).Glycoproteins: Conjugated protein-carbohydrate compounds including mucins, mucoid, and amyloid glycoproteins.Reoviridae: A family of unenveloped RNA viruses with cubic symmetry. The twelve genera include ORTHOREOVIRUS; ORBIVIRUS; COLTIVIRUS; ROTAVIRUS; Aquareovirus, Cypovirus, Phytoreovirus, Fijivirus, Seadornavirus, Idnoreovirus, Mycoreovirus, and Oryzavirus.Virus Attachment: The binding of virus particles to receptors on the host cell surface. For enveloped viruses, the virion ligand is usually a surface glycoprotein as is the cellular receptor. For non-enveloped viruses, the virus CAPSID serves as the ligand.Vesicular stomatitis Indiana virus: The type species of VESICULOVIRUS causing a disease symptomatically similar to FOOT-AND-MOUTH DISEASE in cattle, horses, and pigs. It may be transmitted to other species including humans, where it causes influenza-like symptoms.Gene Products, vpr: Trans-acting proteins which accelerate retroviral virus replication. The vpr proteins act in trans to increase the levels of specified proteins. vpr is short for viral protein R, where R is undefined.vif Gene Products, Human Immunodeficiency Virus: Proteins encoded by the VIF GENES of the HUMAN IMMUNODEFICIENCY VIRUS.Molecular Weight: The sum of the weight of all the atoms in a molecule.Peptide Biosynthesis: The production of PEPTIDES or PROTEINS by the constituents of a living organism. The biosynthesis of proteins on RIBOSOMES following an RNA template is termed translation (TRANSLATION, GENETIC). There are other, non-ribosomal peptide biosynthesis (PEPTIDE BIOSYNTHESIS, NUCLEIC ACID-INDEPENDENT) mechanisms carried out by PEPTIDE SYNTHASES and PEPTIDYLTRANSFERASES. Further modifications of peptide chains yield functional peptide and protein molecules.Cricetinae: A subfamily in the family MURIDAE, comprising the hamsters. Four of the more common genera are Cricetus, CRICETULUS; MESOCRICETUS; and PHODOPUS.Protein Precursorsvpr Gene Products, Human Immunodeficiency Virus: Proteins encoded by the VPR GENES of the HUMAN IMMUNODEFICIENCY VIRUS.Defective Viruses: Viruses which lack a complete genome so that they cannot completely replicate or cannot form a protein coat. Some are host-dependent defectives, meaning they can replicate only in cell systems which provide the particular genetic function which they lack. Others, called SATELLITE VIRUSES, are able to replicate only when their genetic defect is complemented by a helper virus.Poliovirus: A species of ENTEROVIRUS which is the causal agent of POLIOMYELITIS in humans. Three serotypes (strains) exist. Transmission is by the fecal-oral route, pharyngeal secretions, or mechanical vector (flies). Vaccines with both inactivated and live attenuated virus have proven effective in immunizing against the infection.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.Cytomegalovirus: A genus of the family HERPESVIRIDAE, subfamily BETAHERPESVIRINAE, infecting the salivary glands, liver, spleen, lungs, eyes, and other organs, in which they produce characteristically enlarged cells with intranuclear inclusions. Infection with Cytomegalovirus is also seen as an opportunistic infection in AIDS.Closterovirus: A genus of plant viruses in the family CLOSTEROVIRIDAE containing highly flexuous filaments. Some members are important pathogens of crop plants. Natural vectors include APHIDS, whiteflies, and mealybugs. The type species is Beet yellows virus.Bacteriophage N4: A species in the genus N4-like viruses, in the family PODOVIRIDAE, that infects E. coli.Electrophoresis, Polyacrylamide Gel: Electrophoresis in which a polyacrylamide gel is used as the diffusion medium.Influenza A virus: The type species of the genus INFLUENZAVIRUS A that causes influenza and other diseases in humans and animals. Antigenic variation occurs frequently between strains, allowing classification into subtypes and variants. Transmission is usually by aerosol (human and most non-aquatic hosts) or waterborne (ducks). Infected birds shed the virus in their saliva, nasal secretions, and feces.Human Immunodeficiency Virus Proteins: Proteins synthesized by HUMAN IMMUNODEFICIENCY VIRUSES such as the HIV-1 and HIV-2.Gene Products, vif: Retrovirally encoded accessary proteins that play an essential role VIRUS REPLICATION. They are found in the cytoplasm of host cells and associate with a variety of host cell proteins. Vif stands for "virion infectivity factor".Herpesviridae: A family of enveloped, linear, double-stranded DNA viruses infecting a wide variety of animals. Subfamilies, based on biological characteristics, include: ALPHAHERPESVIRINAE; BETAHERPESVIRINAE; and GAMMAHERPESVIRINAE.DNA Viruses: Viruses whose nucleic acid is DNA.Herpes Simplex Virus Protein Vmw65: Trans-acting protein that combines with host factors to induce immediate early gene transcription in herpes simplex virus.Arboviruses: Arthropod-borne viruses. A non-taxonomic designation for viruses that can replicate in both vertebrate hosts and arthropod vectors. Included are some members of the following families: ARENAVIRIDAE; BUNYAVIRIDAE; REOVIRIDAE; TOGAVIRIDAE; and FLAVIVIRIDAE. (From Dictionary of Microbiology and Molecular Biology, 2nd ed)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.TritiumCytoplasm: The part of a cell that contains the CYTOSOL and small structures excluding the CELL NUCLEUS; MITOCHONDRIA; and large VACUOLES. (Glick, Glossary of Biochemistry and Molecular Biology, 1990)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.Nucleocapsid Proteins: Viral proteins found in either the NUCLEOCAPSID or the viral core (VIRAL CORE PROTEINS).Ascoviridae: A family of insect viruses causing disease in lepidopterous larvae, most commonly from species of the owlet moth family Noctuidae. There is one genus: Ascovirus.Rhadinovirus: A genus of the family HERPESVIRIDAE, subfamily GAMMAHERPESVIRINAE, infecting New World primates and other species. HERPESVIRUS 2, SAIMIRIINE is the type species.Bacteriophages: Viruses whose hosts are bacterial cells.Membrane Fusion: The adherence and merging of cell membranes, intracellular membranes, or artificial membranes to each other or to viruses, parasites, or interstitial particles through a variety of chemical and physical processes.Coronaviridae: Spherical RNA viruses, in the order NIDOVIRALES, infecting a wide range of animals including humans. Transmission is by fecal-oral and respiratory routes. Mechanical transmission is also common. There are two genera: CORONAVIRUS and TOROVIRUS.Peptides: Members of the class of compounds composed of AMINO ACIDS joined together by peptide bonds between adjacent amino acids into linear, branched or cyclical structures. OLIGOPEPTIDES are composed of approximately 2-12 amino acids. Polypeptides are composed of approximately 13 or more amino acids. PROTEINS are linear polypeptides that are normally synthesized on RIBOSOMES.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).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.Sindbis Virus: The type species of ALPHAVIRUS normally transmitted to birds by CULEX mosquitoes in Egypt, South Africa, India, Malaya, the Philippines, and Australia. It may be associated with fever in humans. Serotypes (differing by less than 17% in nucleotide sequence) include Babanki, Kyzylagach, and Ockelbo viruses.Genes, gag: DNA sequences that form the coding region for proteins associated with the viral core in retroviruses. gag is short for group-specific antigen.Virus Cultivation: Process of growing viruses in live animals, plants, or cultured cells.RNA Viruses: Viruses whose genetic material is RNA.Fusion Proteins, gag-pol: Polyprotein products of a fused portion of retroviral mRNA containing the gag and pol genes. The polyprotein is synthesized only five percent of the time since pol is out of frame with gag, and is generated by ribosomal frameshifting.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.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.Spodoptera: A genus of owlet moths of the family Noctuidae. These insects are used in molecular biology studies during all stages of their life cycle.Cytidine Deaminase: An enzyme that catalyzes the deamination of cytidine, forming uridine. EC 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.Moloney murine leukemia virus: A strain of Murine leukemia virus (LEUKEMIA VIRUS, MURINE) arising during the propagation of S37 mouse sarcoma, and causing lymphoid leukemia in mice. It also infects rats and newborn hamsters. It is apparently transmitted to embryos in utero and to newborns through mother's milk.Cells, Cultured: Cells propagated in vitro in special media conducive to their growth. Cultured cells are used to study developmental, morphologic, metabolic, physiologic, and genetic processes, among others.RNA-Directed DNA Polymerase: An enzyme that synthesizes DNA on an RNA template. It is encoded by the pol gene of retroviruses and by certain retrovirus-like elements. EC Deletion: A genetic rearrangement through loss of segments of DNA or RNA, bringing sequences which are normally separated into close proximity. This deletion may be detected using cytogenetic techniques and can also be inferred from the phenotype, indicating a deletion at one specific locus.L Cells (Cell Line): A cultured line of C3H mouse FIBROBLASTS that do not adhere to one another and do not express CADHERINS.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)Hemagglutination, Viral: Agglutination of ERYTHROCYTES by a virus.Rauscher Virus: A strain of MURINE LEUKEMIA VIRUS associated with mouse tumors similar to those caused by the FRIEND MURINE LEUKEMIA VIRUS. It is a replication-competent murine leukemia virus. It can act as a helper virus when complexing with a defective transforming component, RAUSCHER SPLEEN FOCUS-FORMING VIRUS.Mutagenesis, Site-Directed: Genetically engineered MUTAGENESIS at a specific site in the DNA molecule that introduces a base substitution, or an insertion or deletion.Centrifugation, Zonal: Centrifugation using a rotating chamber of large capacity in which to separate cell organelles by density-gradient centrifugation. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Haplorhini: A suborder of PRIMATES consisting of six families: CEBIDAE (some New World monkeys), ATELIDAE (some New World monkeys), CERCOPITHECIDAE (Old World monkeys), HYLOBATIDAE (gibbons and siamangs), CALLITRICHINAE (marmosets and tamarins), and HOMINIDAE (humans and great apes).UridineMorphogenesis: The development of anatomical structures to create the form of a single- or multi-cell organism. Morphogenesis provides form changes of a part, parts, or the whole organism.Luteoviridae: A family of RNA plant viruses infecting disparate plant families. They are transmitted by specific aphid vectors. There are three genera: LUTEOVIRUS; Polerovirus; and Enamovirus.Centrifugation, Isopycnic: A technique used to separate particles according to their densities in a continuous density gradient. The sample is usually mixed with a solution of known gradient materials and subjected to centrifugation. Each particle sediments to the position at which the gradient density is equal to its own. The range of the density gradient is usually greater than that of the sample particles. It is used in purifying biological materials such as proteins, nucleic acids, organelles, and cell types.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.Microscopy, Electron, Transmission: Electron microscopy in which the ELECTRONS or their reaction products that pass down through the specimen are imaged below the plane of the specimen.Adenoviruses, Human: Species of the genus MASTADENOVIRUS, causing a wide range of diseases in humans. Infections are mostly asymptomatic, but can be associated with diseases of the respiratory, ocular, and gastrointestinal systems. Serotypes (named with Arabic numbers) have been grouped into species designated Human adenovirus A-F.nef Gene Products, Human Immunodeficiency Virus: Proteins encoded by the NEF GENES of the HUMAN IMMUNODEFICIENCY VIRUS.Orthoreovirus: A genus of the family REOVIRIDAE infecting vertebrates only. Transmission is horizontal and infected species include humans, birds, cattle, monkeys, sheep, swine, baboons, and bats. MAMMALIAN ORTHOREOVIRUS is the type species.Protein Processing, Post-Translational: Any of various enzymatically catalyzed post-translational modifications of PEPTIDES or PROTEINS in the cell of origin. These modifications include carboxylation; HYDROXYLATION; ACETYLATION; PHOSPHORYLATION; METHYLATION; GLYCOSYLATION; ubiquitination; oxidation; proteolysis; and crosslinking and result in changes in molecular weight and electrophoretic motility.Inclusion Bodies, Viral: An area showing altered staining behavior in the nucleus or cytoplasm of a virus-infected cell. Some inclusion bodies represent "virus factories" in which viral nucleic acid or protein is being synthesized; others are merely artifacts of fixation and staining. One example, Negri bodies, are found in the cytoplasm or processes of nerve cells in animals that have died from rabies.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.Avian leukosis virus: The type species of ALPHARETROVIRUS producing latent or manifest lymphoid leukosis in fowl.Host-Pathogen Interactions: The interactions between a host and a pathogen, usually resulting in disease.Nucleoproteins: Proteins conjugated with nucleic acids.Parvoviridae: A family of very small DNA viruses containing a single molecule of single-stranded DNA and consisting of two subfamilies: PARVOVIRINAE and DENSOVIRINAE. They infect both vertebrates and invertebrates.Transfection: The uptake of naked or purified DNA by CELLS, usually meaning the process as it occurs in eukaryotic cells. It is analogous to bacterial transformation (TRANSFORMATION, BACTERIAL) and both are routinely employed in GENE TRANSFER TECHNIQUES.Viruses, Unclassified: Viruses whose taxonomic relationships have not been established.Models, Molecular: Models used experimentally or theoretically to study molecular shape, electronic properties, or interactions; includes analogous molecules, computer-generated graphics, and mechanical structures.Simian virus 40: A species of POLYOMAVIRUS originally isolated from Rhesus monkey kidney tissue. It produces malignancy in human and newborn hamster kidney cell cultures.Plant Viruses: Viruses parasitic on plants higher than bacteria.Viral Fusion Proteins: Proteins, usually glycoproteins, found in the viral envelopes of a variety of viruses. They promote cell membrane fusion and thereby may function in the uptake of the virus by cells.Epitopes: Sites on an antigen that interact with specific antibodies.Genes, vpr: DNA sequences that form the coding region for a trans-activator protein that specifies rapid growth in human immunodeficiency virus (HIV). vpr is short for viral protein R, where R is undefined.Microscopy, Immunoelectron: Microscopy in which the samples are first stained immunocytochemically and then examined using an electron microscope. Immunoelectron microscopy is used extensively in diagnostic virology as part of very sensitive immunoassays.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.Viral Nonstructural Proteins: Proteins encoded by a VIRAL GENOME that are produced in the organisms they infect, but not packaged into the VIRUS PARTICLES. Some of these proteins may play roles within the infected cell during VIRUS REPLICATION or act in regulation of virus replication or VIRUS ASSEMBLY.Avian Sarcoma Viruses: Group of alpharetroviruses (ALPHARETROVIRUS) producing sarcomata and other tumors in chickens and other fowl and also in pigeons, ducks, and RATS.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.Podoviridae: A family of bacteriophages which are characterized by short, non-contractile tails.Cell Fusion: Fusion of somatic cells in vitro or in vivo, which results in somatic cell hybridization.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.Leukemia Virus, Murine: Species of GAMMARETROVIRUS, containing many well-defined strains, producing leukemia in mice. Disease is commonly induced by injecting filtrates of propagable tumors into newborn mice.Ebolavirus: A genus in the family FILOVIRIDAE consisting of several distinct species of Ebolavirus, each containing separate strains. These viruses cause outbreaks of a contagious, hemorrhagic disease (HEMORRHAGIC FEVER, EBOLA) in humans, usually with high mortality.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.Cell Membrane: The lipid- and protein-containing, selectively permeable membrane that surrounds the cytoplasm in prokaryotic and eukaryotic cells.Gene Products, nef: Products of the retroviral NEF GENE. They play a role as accessory proteins that influence the rate of viral infectivity and the destruction of the host immune system. nef gene products were originally found as factors that trans-suppress viral replication and function as negative regulators of transcription. nef stands for negative factor.Archaeal Viruses: Viruses whose hosts are in the domain ARCHAEA.Mutagenesis: Process of generating a genetic MUTATION. It may occur spontaneously or be induced by MUTAGENS.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.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.Chick Embryo: The developmental entity of a fertilized chicken egg (ZYGOTE). The developmental process begins about 24 h before the egg is laid at the BLASTODISC, a small whitish spot on the surface of the EGG YOLK. After 21 days of incubation, the embryo is fully developed before hatching.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.Retroviridae Proteins: Proteins from the family Retroviridae. The most frequently encountered member of this family is the Rous sarcoma virus protein.Herpes Simplex: A group of acute infections caused by herpes simplex virus type 1 or type 2 that is characterized by the development of one or more small fluid-filled vesicles with a raised erythematous base on the skin or mucous membrane. It occurs as a primary infection or recurs due to a reactivation of a latent infection. (Dorland, 27th ed.)Myristic Acids: 14-carbon saturated monocarboxylic acids.Rabbits: The species Oryctolagus cuniculus, in the family Leporidae, order LAGOMORPHA. Rabbits are born in burrows, furless, and with eyes and ears closed. In contrast with HARES, rabbits have 22 chromosome pairs.Amino Acid Substitution: The naturally occurring or experimentally induced replacement of one or more AMINO ACIDS in a protein with another. If a functionally equivalent amino acid is substituted, the protein may retain wild-type activity. Substitution may also diminish, enhance, or eliminate protein function. Experimentally induced substitution is often used to study enzyme activities and binding site properties.Sequence Deletion: Deletion of sequences of nucleic acids from the genetic material of an individual.Pseudorabies: A highly contagious herpesvirus infection affecting the central nervous system of swine, cattle, dogs, cats, rats, and other animals.Orthomyxoviridae: A family of RNA viruses causing INFLUENZA and other diseases. There are five recognized genera: INFLUENZAVIRUS A; INFLUENZAVIRUS B; INFLUENZAVIRUS C; ISAVIRUS; and THOGOTOVIRUS.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.Hemagglutinins, Viral: Specific hemagglutinin subtypes encoded by VIRUSES.Herpesvirus 3, Human: The type species of VARICELLOVIRUS causing CHICKENPOX (varicella) and HERPES ZOSTER (shingles) in humans.Insect Viruses: Viruses infecting insects, the largest family being BACULOVIRIDAE.Vaccinia: The cutaneous and occasional systemic reactions associated with vaccination using smallpox (variola) vaccine.Electron Microscope Tomography: A tomographic technique for obtaining 3-dimensional images with transmission electron microscopy.Nucleopolyhedrovirus: A genus of the family BACULOVIRIDAE, subfamily Eubaculovirinae, characterized by the formation of crystalline, polyhedral occlusion bodies in the host cell nucleus. The type species is Autographa californica nucleopolyhedrovirus.Genetic 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.Antibodies, Neutralizing: Antibodies that reduce or abolish some biological activity of a soluble antigen or infectious agent, usually a virus.Antibodies, Monoclonal: Antibodies produced by a single clone of cells.