Myxomatosis: passive immunity in the offspring of immune rabbits (Oryctolagus cuniculus) infested with fleas (Spilopsyllus cuniculi Dale) and exposed to myxoma virus. (1/1518)

Kittens with maternal antibodies to myxoma virus, the offspring of rabbits which had recovered from myxomatosis, were exposed to fleas contaminated with myxoma virus and/or contact with infected rabbits from birth. All kittens died or became infected before 8 weeks of age. When compared with adult animals similarly infected the kittens showed no advantage in terms of survival time or recovery rate attributable to maternal antibodies. Flea transmission of virus was found more effective than contact transmissions.  (+info)

Thylakoid membrane polypeptides of Chlamydomonas reinhardtii: wild-type and mutant strains deficient in photosystem II reaction center. (2/1518)

Unstacked thylakoid membrane vesicles were obtained from a homogenate of Chlamydomonas reinhardtii by flotation in a 1.8 M sucrose layer containing 5 mM HEPES (N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid)-10 mM EDTA (pH 7.5). Sodium dodecyl sulfate-gradient gel electrophoresis showed that the wildtype membranes have a total of at least 33 polypeptides ranging in molecular weights from 68,000 to less than 10,000. The wild-type and three non-photosynthetic mutant strains were studied with respect to their photosynthetic electron transport properties, their fluorescence rise kinetics, and their membrane polypeptide compositions. The results showed a strong correlation between the presence of a membrane polypeptide (molecular weight = 47,000) and the activity of the photosystem II reaction center. This polypeptide is missing from F34 (a mendelian mutant lacking Q, the primary electron acceptor of photosystem II), but is partially restored in a suppressed strain of F34 in which there is an incomplete recovery of photosystem II activity. In a thermosensitive mutant, T4, the same polypeptide is present in reduced amount only in cells grown at 35 degrees but not in those grown at 25 degrees. Evidence from fluorescence rise kinetics and partial photochemical reactions show that the cells grown at 25 degree are similar to wild-type cells but the cells grown at 35 degrees are greatly deficient in Q.  (+info)

Differential distribution of novel restriction-modification systems in clonal lineages of Neisseria meningitidis. (3/1518)

Using representational difference analysis, we isolated novel meningococcal restriction-modification (R-M) systems. NmeBI, which is a homologue of the R-M system HgaI of Pasteurella volantium, was present in meningococci of the ET-5 complex and of lineage III. NmeAI was found in serogroup A, ET-37 complex, and cluster A4 meningococci. NmeDI was harbored by meningococci of the ET-37 complex and of cluster A4, but not by serogroup A meningococci. Two of the R-M systems, NmeBI and NmeDI, were located at homologous positions between the phenylalanyl-tRNA synthetase genes pheS and pheT, which appeared to be a preferential target for the insertion of foreign DNA in meningococci. The distribution of the three R-M systems was tested with 103 meningococcal strains comprising 49 sequence types. The vast majority of the strains had either NmeBI, NmeAI, or both NmeAI and NmeDI. Using cocultivation experiments, we could demonstrate that NmeBI, which was present in ET-5 complex meningococci, was responsible for a partial restriction of DNA transfer from meningococci of the ET-37 complex to meningococci of the ET-5 complex.  (+info)

HOBACGEN: database system for comparative genomics in bacteria. (4/1518)

We present here HOBACGEN, a database system devoted to comparative genomics in bacteria. HOBACGEN contains all available protein genes from bacteria, archaea, and yeast, taken from SWISS-PROT/TrEMBL and classified into families. It also includes multiple alignments and phylogenetic trees built from these families. The database is organized under a client/server architecture with a client written in Java, which may run on any platform. This client integrates a graphical interface allowing users to select families according to various criteria and notably to select homologs common to a given set of taxa. This interface also allows users to visualize multiple alignments and trees associated to families. In tree displays, protein gene names are colored according to the taxonomy of the corresponding organisms. Users may access all information associated to sequences and multiple alignments by clicking on genes. This graphic tool thus gives a rapid and simple access to all data required to interpret homology relationships between genes and distinguish orthologs from paralogs. Instructions for installation of the client or the server are available at http://pbil.univ-lyon1. fr/databases/hobacgen.html.  (+info)

A technique for the isolation of mutants of Escherichia coli affected in degradation of cellular RNA. (5/1518)

Using a semiautomatic technique for handling large numbers of Escherichiacoli colonies, mutants that fail to digest their cellular RNA were isolated. This was achieved by using multiwell plates where each colony is cloned in an individual well. Cells labeled with a radioactive RNA precursor were starved for a carbon source at a high temperature. In order to assess whether or not degradation of cellular RNA took place, aliquots of each culture were subjected to autoradiography. A number of mutants defective in decay of RNA were isolated. One of them was characterized, and was found to be deficient specifically in the enzyme polynucleotide phosphorylase. Experiments carried out with this strain indicate that this enzyme participates in the degradation of "stable" RNA during carbon starvation.  (+info)

Identification and characterization of the in vitro synthesized gene products of bacteriophage M13. (6/1518)

Bacteriophage M13 replicative form (RF) DNA was used to direct coupled transcription and translation in cell-free extracts prepared from Escherichia coli. By using RF DNA, isolated from cells infected with appropriate amber mutants of this phage, it has been possible to identify the products of genes I through IV. By using the same methods no gene-product relationship could be demonstrated for genes VI and VII. Coupled in vitro protein synthesis studies on RF-III DNA, a linear double-stranded DNA molecule, obtained after cleavage of either RF-I or RF-II DNA with the restriction endonuclease R.Hin11 from Haemophilus influenzae, indicated that the cleavage site for this enzyme is located in gene II. The in vitro products of both gene III and gene VIII are about 30 and six amino acids longer, respectively, than their native counterparts present within the virion. These results suggest that the latter proteins arise in vivo by cleavage of precursor molecules. Coupled transcription and translation studies on a DNA fragment which only contained the genetic information coding for gene IV protein, obtained after cleavage of RF DNA with the restriction endonuclease R.Hap11 from Haemophilus aphirophilus, indicated that a large number of the in vitro synthesized polypeptides are the result of premature chain termination.  (+info)

Bacteriophage-host interaction and restriction of nonglucosylated T6. (7/1518)

Nonglucosylated T6 phage (T6gtam 16am30, hereafter called T6alpha gt-) were found to have two structural anomalies when compared with wild-type T6. The DNA of T6alpha gt- phage contains single-strand interruptions. These can be seen both during infection, in the pool of replicating DNA, and in DNA extracted from purified phage. In addition, the sodium dodecyl sulfate-polyacrylamide gel pattern of T6alpha gt- phage structural proteins reveals a protein band not found in T6. The altered protein has a mobility slightly faster than that of the major head protein, and it is not removed by osmotic shock. The restriction activity of Escherichia coli B directed against T6alpha gt- phage is abolished by preinfection of the cells for 4 min with T4 im m2. The shut-off of restriction is observed either by the rescue of superinfecting T6alpha gt- or by the failure to detect degradation of incoming T6alpha gt- DNA. This effect is resistant to rifampin and chloramphenicol.  (+info)

Endonucleolytic incision of x-irradiated deoxyribonucleic acid by extracts of Escherichia coli. (8/1518)

An enconuclease activity that reacts with x-irradiated DNA is present in extracts of E. coli. By using centrifugal methods to monitor the conversion of the supercoiled, circular double-stranded DNA for phage phi-x-174 (replicative form) or PM2 to the relaxed circular form it was possible to quantitate the rate of radiation induced endonuclease-sensitive sites in the DNA. For every single-strand break induced by x-rays under aerobic irradiation conditions, there is approximately one induced site sensitive to this endonuclease activity. Under irradiation conditions (addition OF Potassium iodide) that dramatically reduce rates of single-strand breaks and "alkalilabile" lesions, the number of endonuclease-sensitive sites relative to single-strand breaks increase approximatley 4-fold. This nuclease is present in several strains of E. coli B and K12, including mutants deficient in DNA polymerase I, recombination gene products (rec mutants), ultraviolet light incision enzyme (uvr A mutant), and endonuclease II. It is suggested that this endonuclease may be involved in an excision repair process for damages incurred in DNA by ionizing radiation.  (+info)