Pathways for repair of DNA damaged by alkylating agent in Escherichia coli

A strain with both the polA12 and the alk-1 mutation is only slightly more sensitive to methyl methane sulfonate (MMS) than isogenic strains with only one of the mutations. On the other hand, alk-1 recA1 double mutant is much more sensitive to MMS than are strains carrying either one of alk or recA mutation. It was suggested that the alk and the polA gene products are involved in the same DNA repair process whereas the recA function is independent from the process. The yield of MMS-induced mutation (Arg- (argE) to Arg+ reversion) in alk mutant is considerably higher than that in wild type strain. Thus, the repair process in which the alk gene product is involved is relatively accurate. When MMS-treated lambda phages were plated on MMS-treated bacteria, there were considerable increases in survival of treated phage even in recA alk double mutant. It seems that a new repair pathway, which is specific for alkylating agent-induced damages and is not dependent on the RecA function, may be induced on exposure of bacteria to the alkylating agent.