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At least 1,549 records · Page 86Linked to original sources
PubMed1969

R factors improving survival of Escherichia coli K-12 after ultraviolet irradiation.

Two R factors which have the capacity to improve survival of some strains of Escherichia coli K-12 by approximately 60% after ultraviolet light have been identified and characterized. Both are fi(-), but neither produce colicins. The ability to enhance survival can be separated from all other identified R-factor functions. Improved survival does not result from improved excisional capacity, but does require an intact host capacity for genetic recombination. No effects on host cell growth or postirradiation lag were observed. A proposed mechanism of action is described.

Cell Division↗
PubMed1969

Identification of closely linked loci controlling ultraviolet sensitivity and refractivity to colicin E2 in Escherichia coli.

Mutants (phenotypic symbol Ref-II) refractory to colicin E2 have been isolated in several strains of Escherichia coli K-12, and a refII locus has been mapped 1 to 2 min counter clockwise to thr. A small number of Ref-II mutants are also ultraviolet (UV)-sensitive and the uv(s) locus in one such strain has been mapped close to the refII locus near thr. The Ref-II mutation alone does not affect recombinant formation in F(-) strains, but the Ref-II, UV(s) strains behave in many respects like Rec(-) mutants, giving reduced recombination frequencies in crosses with male strains. It is suggested that the refII and uv(s) loci correspond to closely linked if not identical genes, concerned in some way in the activity of one or more deoxyribonucleases, and that the Ref-II, UV(s) mutants arise as the pleiotropic expression of a single gene or of a deletion or polar mutation affecting linked genes.

Chromosome Mapping↗
PubMed1969

Some properties of excision-defective recombination-deficient mutants of Escherichia coli K-12.

Strains of Escherichia coli that carry the mutation uvrA6 show no measurable excision of pyrimidine dimers and are easily killed by ultraviolet (UV) light, whereas strains that carry recA13 are defective in genetic recombination and are also UV-sensitive. An Hfr strain carrying uvrA6 was crossed with an F(-) strain carrying recA13. Among the recombinants identified, one carrying uvrA recA proved to be of exceptional sensitivity to UV light. It is estimated from the UV dose (0.2 erg/mm(2) at 253.7 nm) required to reduce the number of colony-forming cells by one natural logarithm that about 1.3 pyrimidine dimers were formed in a genome of 5 x 10(6) base pairs for each lethal event. This double mutant is 40 times more UV-sensitive than the excision-defective strain carrying uvrA6. The replication of one pyrimidine dimer is generally a lethal event in strains carrying recA13. Spontaneous breakdown and UV-induced breakdown of the deoxyribonucleic acid (DNA) of cells of the various genotypes were estimated by growing the cells in medium containing (3)H-thymidine and measuring both acid-precipitable and acid-soluble radioactivity. The UV-induced degradation in strains with recA13 did not require the uvr(+) genes and hence appears to depend upon a mechanism other than dimer excision. The greater level of survival after irradiation in Rec(+) as compared to Rec(-) bacteria may be due to a recovery mechanism involving the reconstruction of the bacterial chromosome through genetic exchanges which occur between the newly replicated sister duplexes and which effectively circumvent the damaged bases remaining in the DNA.

Conjugation, Genetic↗
PubMed1989

Failure to induce a DNA repair gene, RAD54, in Saccharomyces cerevisiae does not affect DNA repair or recombination phenotypes.

The Saccharomyces cerevisiae RAD54 gene is transcriptionally regulated by a broad spectrum of DNA-damaging agents. Induction of RAD54 by DNA-damaging agents is under positive control. Sequences responsible for DNA damage induction (the DRS element) lie within a 29-base-pair region from -99 to -70 from the most proximal transcription start site. This inducible promoter element is functionally separable from a poly(dA-dT) region immediately downstream which is required for constitutive expression. Deletions which eliminate induction of RAD54 transcription by DNA damage but do not affect constitutive expression have no effect on growth or survival of noninducible strains relative to wild-type strains in the presence of DNA-damaging agents. The DRS element is also not required for homothallic mating type switching, transcriptional induction of RAD54 during meiosis, meiotic recombination, or spontaneous or X-ray-induced mitotic recombination. We find no phenotype for a lack of induction of RAD54 message via the damage-inducible DRS, which raises significant questions about the physiology of DNA damage induction in S. cerevisiae.

Base Sequence↗
PubMed1991

A review of forty-five years study of Hiroshima and Nagasaki atomic bomb survivors. Biochemical genetics study.

After 40 years of studies on the children of atomic bomb survivors and a suitable control population in which no statistically significant genetic effects of A-bomb radiation were observed, two new projects have been initiated in order to detect mutations in the DNA and RNA molecules. Permanent cell lines from peripheral B-lymphocytes from approximately 500 families composed of exposed parents and their children and approximately 500 control families are being established by Epstein-Barr virus transformation. Cells will be sources for DNA and RNA samples in the screening for mutations. After comparison of efficiencies of the scanning techniques, we selected the denaturing gradient gel electrophoresis (DGGE) of DNA fragments amplified by polymerase chain reaction (PCR) for our purpose. A small scale pilot study has started to solve problems and obtain a better efficiency in this approach. Current thinking about the most efficient procedures is presented.

Humans↗
PubMed1975

Feathery outbrusts of the colonies of Clostridium sporogenes containing chain forming mutants after ultraviolet irradiation.

Cl. sporogenes NCTC 532 was irradiated with UV light, 20 mins. irradiated colonies after initial 48 hours incubation at 37 degrees C and 10-20 days ageing at room temperature (22 to 25 degrees C), gave rise to feathery outbrusts. The material from these outbursts grew in long chains in fluid media. A pure chain - forming culture could not be obtained as the single cells or pairs always "contaminated" the chain - forming culture.

Cell Adhesion↗