Effects of a short heat pulse on phenomena related to DNA repair in ultraviolet-irradiated Escherichia coli.

Mutational synergism between heat and UV light in Escherichia coli was examined for evidence supporting various possible synergistic mechanisms. UV and heat lethality were only additive or slightly synergistic after 30 sec at 50 degrees C. The order of treatment did not affect the mutational synergism. Synergism is not peculiar to induction of mutation from streptomycin sensitivity to resistance. Neither DNA breakage nor alteration of post-replication repair rates was seen after a 5 min 50 degrees C heat pulse. Synergism was observed with temperatures as low as 43 degrees C. A strain deficient in excision repair but not post-replication repair exhibited mutational synergism, suggesting that synergism may involve the differential heat alteration of the error-prone post-replication repair process.