Induction of error-prone repair as a consequence of DNA ligase deficiency in Escherichia coli.

DNA ligase deficiency is shown to induce generalized mutator activity in E. coli. This mutator activity is unaffected by 3 mug/ml of chloramphenicol but is abolished both in lig-recA double mutants and by incubation with 20 mug/ml of chloramphenicol. Dna ligase deficiency is also shown to reactivate ultraviolet light-irradiated phage lambda and T7 and to increase both spontaneous and ultraviolet light-induced mutagenesis in phage lambda, all of which are abolished in lig-recA strains. Interaction occurs between the molecular events of mutagenesis induced by ultraviolet irradiation and those induced by DNA ligase deficiency. These observations suggest a common pathway, coordinately expressed with the inducible repair mode, that is responsible for mutagenesis.