| This study addresses the possible function of the Escherichia coli dinB gene in spontaneous and UV-induced mutagenesis and DNA repair triggered by UV-induced damage. The trpA reversion system was used to study spontaneous and UV mutagenesis. This system involved strains carrying specific trpA alleles. Revertants were selected that had regained the wild-type phenotype of synthesizing tryptophan. The trpA spontaneous and UV-induced revertants were sequenced, and the molecular nature of the original mutations and of the revertants was determined. The dinB allele, the umuC allele, and the combination of both were examined for their effect on spontaneous and UV mutagenesis. The results show that dinB was not significantly involved in spontaneous and UV mutagenesis. The involvement of DinB and UmuC in UV survival was studied through a 20-hour period of growth. It appears that DinB and UmuC were essential for UV repair and cell survival in the log phase of growth. The effect of dinB on UV survival and UV mutagenesis was dependent upon an active umuC allele. In contrast to the dinB strain with a polar deletion mutation that showed a higher level of UV sensitivity, a dinB strain with a missense nonpolar mutation showed no UV sensitivity. This suggests that either a downstream gene from dinB is actually responsible for protection from UV damage or the function of DinB is not dependent upon its polymerase activity. |
