Stimulation of DNA synthesis in bacterial DNA--membrane complexes after low doses of ionizing radiation

DNA--membrane complexes from three strains of E. coli were irradiated and changes in the rates of DNA synthesis were observed. Doses from 1--10 krad to complexes from W3110 and pol A1 strains gave up to a 100 per cent increase in DNA synthesis; under the same conditions, no change was observed in Bs-1. The degree of stimulation did not depend on the presence of oxygen during irradiation, and a post-irradiation incubation was necessary to achieve activation. The properties of all three complexes were similar when unirradiated. Irradiation of intact organisms under conditions which produced marked, oxygen-dependent inhibition of the Bs-1 complex had no significant effect on those from W3110 and Pol A1. Enhanced DNA synthesis is concluded to be due wholly to repair of preexisting DNA. It is further postulated that DNA synthesis in untreated complexes (E. coli B's, W3110 and Pol A1) is mainly of the repair-type and does not necessarily take place at the site of DNA--membrane attachment.