Mutagenic DNA repair in Escherichia coli. XVIII. Involvement of DNA polymerase III alpha-subunit (DnaE protein) in mutagenesis after exposure to UV light.

UV light was unable to induce rifampicin-resistant mutations at 43 degrees C in Escherichia coli ER11 dnaE486. Although DnaE486 gene product is inactive at 43 degrees C, these bacteria contain the pcbA1 mutation which allows DNA replication provided DNA polymerase I is functional. The experiments were carried out under conditions where full expression of rifampicin-resistant mutations could occur so that the lack of induced mutations cannot be ascribed to an effect of incubation at 43 degrees C on mutation expression. UV-mutability at 43 degrees C was restored by the presence of the dnaE+ allele on a plasmid. It is concluded that functional DnaE protein is essential for UV mutagenesis. The dnaE486 mutation also blocked the induction at 43 degrees C of mutations induced by UV plus delayed photoreversal, a procedure that has been postulated to reflect an early misincorporation step in the UV mutagenic process.