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D Billen

Publications and source records attributed to D Billen.

At least 37 records · Page 2Linked to original sources
PubMed1973

Genetic analysis of repair of ultraviolet damage by competent and noncompetent cells of Bacillus subtilis.

The repair of ultraviolet (UV) damage in Bacillus subtilis W23T(-) has been studied by transformation with deoxyribonucleic acid (DNA) extracted from irradiated cells before and after repair. The extent of repair of genetic markers by donor cells after low or moderate doses of UV was found to be related only to the initial degree of inactivation. After a very high dose, further inactivation occurred, also in proportion to initial damage. In addition, the competent recipient cells were shown to repair approximately 75% of the damage in transforming DNA. The sensitivities of markers irradiated either in vivo or in vitro appeared to be related to map position, the more proximal markers showing a greater resistance to UV inactivation.

Bacillus subtilis↗
PubMed1972

Gene frequency analysis of chromosomal initiation sites in Bacillus subtilis after ultraviolet light or x-ray exposure.

Bacillus subtilis was exposed to ultraviolet light (UV) or X rays, and gene frequency analysis was used to study the location of initiation sites of postirradiation deoxyribonucleic acid (DNA) synthesis. It was found that DNA synthesis resumes primarily from the origin after UV exposure. With X irradiation, the origin is not selectively replicated. Elevated origin-to-terminal marker ratios observed after UV exposure of exponentially growing cells were interpreted as evidence for selective UV resistance of the replicative origin region of the bacterial chromosome.

Bacillus subtilis↗
PubMed1971

Evidence suggestive of compartmentalization of deoxyribonucleic acid-synthesizing systems in freeze-treated Bacillus subtilis.

Freezing of Bacillus subtilis in liquid nitrogen results, upon thawing of the cells, in an enhanced deoxyribonucleoside triphosphate and reduced thymidine (Tdr) incorporation into cellular deoxyribonucleic acid (DNA). The DNA synthesized from thymidine triphosphate (TTP) was made by a "repair"-type system as determined by density transfer experiments. The mono- and diphosphate precursors were also incorporated by a "repair"-type synthesis. When Tdr was used as the radioactive precursor in the assay mixture, the product was only that expected from a semiconservative synthesis. Superlethal ultraviolet light exposure of the freeze-treated cells stimulated incorporation of phosphorylated precursors into DNA. Tdr uptake was greatly reduced by ultraviolet exposure, and only repair synthesis was observed. TTP and Tdr do not compete with one another in this system. The possibility that two DNA synthesizing systems exist in separate, non-mixing cellular compartments is considered.

Bacillus subtilis↗
PubMed1970

The dampening of DNA replication cycles after x-irradiation or ultraviolet irradiation.

Escherichia coli strains 15T(-) (555-7) and B/r were grown in the presence of thymine-(14)C to label all DNA. The ability of these parental DNA's to undergo cycles of replication subsequent to cellular irradiation with either X-ray or ultraviolet light (UV) was followed with density labels. Exposed cells were shifted into the density medium at times which were approximately multiples of normal rounds of DNA replication. A portion of the parental DNA, replicated semiconservatively once during an initial cycle following UV or X-irradiation in E. coli, failed to replicate again within the time studied. The time course of semiconservative parental DNA replication is altered.

Carbon Isotopes↗
PubMed1970

Relationship between radiation response and the deoxyribonucleic acid replication cycle in bacteria: dependence on the excision-repair system.

Prestarvation of Escherichia coli for required amino acids results in a marked enhancement in both ultraviolet light (UV) or X-ray resistance for selective strains. Preventing protein synthesis by starvation for required amino acids results in completion of the cycle of chromosomal replication then underway. We have investigated the relationship between starvation-induced resistance enhancement (SIRE) and the excision-repair (Hcr) system in several E. coli strains including E. coli B/r hcr(+) and its isogenic mutant E. coli B/r hcr(-). The following observations were made. (i) The Hcr system is the major component of SIRE in UV-irradiated strain B/r. By using the Hcr(+) strain, SIRE increases the 10% survival dose from approximately 400 ergs to approximately 1,200 ergs/mm(2). With the Hcr cells, the increase is from approximately 45 ergs to 60 ergs/mm(2). (ii) Although prestarvation leads to a moderate enhancement of resistance to X irradiation, this effect is not dependent on the Hcr system. (iii) The double mutant, E. coli B(s-1) (hcr(-)exr(-)) is completely unable to express SIRE whether studied with UV or X irradiation. It is concluded that the Hcr system is the major system responsible for SIRE in UV-treated cells, whereas Exr (resistance to X rays) may be involved to a minor extent. The Exr character appears to be required for SIRE expression in X-ray exposed cells.

Amino Acids↗
PubMed1969

Saturation of dark repair synthesis: accumulation of strand breaks.

Reversal of ultraviolet light damage to DNA by the dark repair system is limited. Experiments utilizing density and radioactive labels demonstrated that repair synthesis is not proportional to dose at doses above 200 ergs/mm(2). In addition, the number of residual excision induced gaps in Escherichia coli B/r hcr(+) DNA increases with higher UV doses. The extent of repair is apparently limited by saturation of the repair synthesis step.

Carbon Isotopes↗