The role of DNA polymerase I in pyrimidine dimer excision and repair replication in Escherichia coli K12 following ultraviolet irradiation

Abstract

The ability of three different DNA polymerase I mutants of Escherichia coli to carry out excision repair was examined. Strains having the same genetic origin but carrying either the polA1, polA107, resA1 or pol + alleles were compared. The rate of ultraviolet-induced dimer excision was slightly reduced, relative to that found in Pol + strains, in the PolA1 strain; greatly reduced in the PolA107 strain; and found not to occur in the ResA1 strain. Ultraviolet light-induced repair synthesis as determined by the ultravioletstimulated incorporation of 3H-labelled 5-bromo-2′-deoxyuridine into DNA of the parental density showed that the polA1 mutation results in an increase in repair replication while the presence of the polA107 allele caused a reduction in the amount of repair synthesis relative to that of the Pol + strain. The ResA1 strain, however, showed no ultraviolet stimulation of the incorporation of the density label. This observation indicates that DNA polymerase I plays a key role in the excision repair process in E. coli.