Effect of some pre-treatments on UV-sensitivity and on the course of macromolecular synthesis inEscherichia coli 15 T⁻, U⁻, his⁻

Abstract

The UV-sensitivity ofEscherichia coli 15 T⁻, U⁻, his⁻ cells after a 45 minutes glucose, thymine uracil, or histidine pre-irradiation starvation, as well as the course of DNA, RNA, and protein synthesis during starvation and during a 60 minute post-treatment in a complete medium were investigated. An increased radioresistance was observed when starvation for some compounds resulted in a consequent inhibition of protein synthesis, as it was observed in the case of glucose, histidine, or uracil starvation. During thymine starvation, which led to a decreased resistance, no inhibition of protein synthesis was recorded. The postirradiation time-course of DNA synthesis did not show any correlation with the increased rate of resistance. The DNA synthesis after U⁻ pre-treatment was greatly delayed, however, after glucose pre-treatment no retardation was observed although both factors increased the rate of surviving cells approximately to the same extent. We assume that the factors which increase the radio-resistance could act by a similar mechanism which would take part in the inhibition of protein synthesis. This mechanism could consist in a decrease of the m-RNA turnover.