Mutagenic DNA repair in Escherichia coli. III. Requirement for a function of DNA polymerase III in ultraviolet-light mutagenesis.

The polC (= dnaE) temperature-sensitive DNA polymerase III mutation from Escherichia coli BT1026 has been transduced into E. coli WP2 (to give CM731) and WP2 uvr A (to give CM741). In excision-deficient CM741 UV-induced Trp+ mutations progressively lost their photoreversibility during post-irradiation incubation at 34 degrees. Immediately after transfer to 43 degrees, however, there was no further loss of reversibility although post-replication strand joining still occurred and uptake of 3H-thymidine into DNA continued for 20 to 30 min. In excision-proficient CM731, UV lesions capable of leading to Strr mutations disappeared during post-irradiation incubation at restrictive temperature and there was no increase in the number remaining after exposure to photoreversing light. In contrast, at permissive temperature, premutational lesions were not lost and became progressively converted into non-photoreverisble mutations. It is concluded that a function of the polC gene is necessary for error-prone repair to occur and that this function is defective at 43 degrees in the enzyme specified by the polC allele from BT1026. This function seems not to be essential for most post-replication or excision repair or for normal DNA replication and may be particularly involved in the insertion of incorrect bases during error-prone repair.