Synthesis of nucleic acids in ultraviolet-treated Escherichia coli

Abstract

1. 1. The effect of various wavelengths of ultraviolet (UV) radiation upon the synthesis of nucleic acids in cultures of Escherichia coli B in logarithmic (log) and out-of-log phases of the growth cycles was studied. 2. 2. Treatment of cultures of log phase E. coli B with UV radiation of 254 mμ stops desoxyribonucleic acid (DNA) synthesis immediately, whereas ribonucleic acid (RNA) synthesis continues for about one division cycle (30 minutes) afterwards. 3. 3. Treatment of out-of-log phase cultures of E. coli B with these radiations stops DNA and RNA synthesis immediately, as does treatment with UV of 265 mμ. 4. 4. After irradiation with UV of λ 226 mμ the synthesis of RNA and DNA is not delayed as compared to the controls. 5. 5. RNA and DNA synthesis, stopped by UV, is resumed first in the cultures subsequently illuminated with white light, indicating photoreversal of UV injury by white light, and then in the UV-treated cultures. In both cases, synthesis of nucleic acid is resumed at about the time that the bacteria begin to divide. 6. 6. Since RNA synthesis is inhibited by UV (254 mμ or 265 mμ) in E. coli cultures in the out-of-log phases of the growth cycle but not in the log phase cultures, two loci of action of UV radiations on RNA synthesis are suggested. Citations supporting this view are discussed. 7. 7. The decline in viability of E. coli B after irradiation with very short UV (226 mμ) without a corresponding decrease in RNA and DNA synthesis suggests a locus of action of these radiations on the cell different from the part of the cell involved in nucleic acid synthesis.