Gene Frequency Analysis of Chromosomal Initiation Sites in Bacillus subtilis after Ultraviolet Light or X-Ray Exposure

Abstract

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. This laboratory has been engaged in studies aimed at defining the quantitative and regulatory aspects of chromosome replication after ultraviolet light (UV) or X-ray challenge to bacterial cells. By using a combination of density and radioisotopic labeling techniques, it was previously shown (4) that, when bulk deoxyribonucleic acid (DNA) synthesis re

Genetic Analysis of Repair of Ultraviolet Damage by Competent and Noncompetent Cells of Bacillus subtilis

“…Our data show clearly that there are no large regions preferentially repaired by W23T-, although we cannot rule out favored sites or polarity over very short regions. The rapidity of repair in stationaryphase cells rules out any dependence on an active replication complex; furthermore, even moderate doses of UV (400 ergs/mm2) cause a marked lag in DNA synthesis (6). The best interpretation of the data is that the probability of repair of any damage site is the same as for any other site, and independent of other factors such as local structure of the DNA, packaging of the DNA, etc.…”

“…Incubation with DNA was carried out for 20 to 60 min at 37 C and terminated by exposure to 10 Ag of deoxyribonuclease per ml. Transformants were plated on the solid medium described previously (6).…”

“…It has been shown that in Bacillus subtilis (6) and in Escherichia coli (4) ultraviolet (UV) irradition of log-phase cells results in reinitiation of deoxyribonucleic acid (DNA) synthesis from the fixed origin. In contrast, X-ray treatment appears to cause initiation of replication from non-origin sites (4, 6; D. Billen, unpublished observations).…”