UV-inducible repair: influence on survival, dimer excision, DNA replication and breakdown in Escherichia coli B/r Her+ cells.

Using a model of double-UV-irradiation with inducing1 (non-lethal) and lethal fluences2 we have studied involvement of UV-inducible functions in post-UV-irradiation restoration processes and survival of Escherichia coli B/r thy-trp-Hcr+. Cells irratiated with both inducing and lethal fluences differed from cells irradiated with lethal fluence in the following respects: They were more UV resistant; they did not die during postincubation with chloramphenicol3; they exhibited a significant reduction in dimer excision; they were able to resume DNA replication and produce normal-sized DNA molecules in the presence of chloramphenicol. Since induction was provoked in cell prestarved for amino acids it was not associated with damage to points active in replication. However, the inducible product was more important for repair of replicating than non-replicating cells. The data indicate that protein necessary for resumption of DNA synthesis after UV is not constitutive but inducible.