DNA synthesis in UV-irradiated Escherichia coli K-12 strains carrying dnaA mutations.

It has been found that UV irradiation of dnaA mutants of E. coli K-12 enables the initiation of DNA synthesis at a temperature restrictive to these mutants. The UV-induced DNA synthesis is dependent on protein synthesis and on a transcriptional event at a time when protein synthesis is no longer required. In contrast to dnaA mutants UV irradiation fails to induce DNA synthesis in the two other initiation mutants dnaC2 and dnaB252. DNA synthesis at the restrictive temperature is initiated also when the tif-1 phenotype is expressed in the dnaA46 tif-1 double mutant. Possible mechanisms of the observed capability of dnaA mutants to synthesize DNA at the restrictive temperature after UV irradiation or under conditions of tif-1 expression are discussed.