Two ultraviolet light (UV)-sensitive mutants have been isolated from Escherichia coli K-12. These mutants, designated RuvAand RuvB-, were controlled by a gene located close to the his gene on the chromosome map. They were sensitive to UV (10to 20-fold increase) and slightly sensitive to gamma rays (3fold increase). Host cell reactivation, UV reactivation and genetic recombination were normal in these mutants. Irradiation of the mutants with UV resulted in the production of single-strand breaks in deoxyribonucleic acid, which was repaired upon incubation in a growth medium. After UV irradiation, these mutants resumed deoxyribonucleic acid synthesis at a normal rate, as did the parent wild-type bacteria, and formed nonseptate, multinucleate filaments. From these results we concluded that the mutants have some defect in cell division after low doses of UV irradiation, similar to the Ion or fil + mutant of E. coli. The ruv locus was divided further into ruvA and ruvB with respect to nalidixic acid sensitivity and the effect of minimal agar or pantoyl lactone on survival of the UV-irradiated cell. The ruvB -mutant was more sensitive to nalidixic acid than were ruvAand the parent strain. There was a great increase in the surviving fraction of the UV-irradiated ruvBmutant when it was plated on minimal agar or L agar containing pantoyl lactone. No such increase in survival was observed in the ruvA mutant. Biochemical pathways involved in the process for septum formation and cell division are not well understood. One approach to this problem is isolation of conditional cell division mutants which are temperature dependent or defective in cell division, after very mild ultraviolet light (UV) irradiation or treatment with deoxyribonucleic acid (DNA) synthesis inhibitors. Studies on the biochemical basis of their failure to divide would provide useful information on the normal regulation of cell division. 7.4. Galactose was sterilized separately and mixed with the medium at a final concentration of 0.3%.The composition of M buffer, minimal (M) medium, and enriched M (EM) medium are described elsewhere (17).UV and gamma-ray irradiation. A 15-W Toshiba germicidal lamp was used as the source of UV light. 337 on August 6, 2020 by guest
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