RESUMO
The frequency of spontaneous as well as induced reversions of auxotrophic mutations in Escherichia coli AB1157 and its DeltadnaK and DeltadnaKdnaJ derivatives was estimated. The obtained results demonstrate that both mutants tested are characterized by elevated frequency of spontaneous reversions compared to their AB1157 parent. In contrast, the frequency of reversions induced by UV and MMS, i.e. agents inducing the SOS response, is reduced in DeltadnaJ and DeltadnaKdnaJ mutants, pointing to the possible defect of these mutants in error prone repair. Due to the fact that UmuC protein is one of the main players executing the error prone repair, its stability in DeltadnaJ and DeltadnaKdnaJ mutants was also studied. Reduced UmuC stability was demonstrated only in the DeltadnaKdnaJ mutant.