DNA repair in Escherichia coli mutants deficient in DNA polymerases I, II and-or 3.

Abstract

E. coli mutants deficient in DNA polymerase I, in DNA polymerases I and II, or in DNA polymerase III, can efficiently and completely execute excision repair and post-replication repair of UV-damaged DNA at 43 degrees when assayed by alkaline sucrose gradients. Repair by cells deficient in polymerase I and in polymerases I and II is inhibited by 1-beta-D-arabinofuranosylcytosine at 43 degrees , whereas that by cells deficient in polymerase III is insensitive to the inhibitor. When both DNA polymerases I and III are deficient, both excision repair and post-replication repair are greatly reduced at 43 degrees , and the residual repair capability is inhibited by 1-beta-D-arabinofuranosylcytosine. Very little dark repair is observed in cells deficient in DNA polymerases I, II, and III, and the DNA is extensively degraded. These results suggest that either DNA polymerase I or DNA polymerase III is required for complete and efficient repair, and that when both DNA polymerases I and III are deficient, DNA polymerase II mediates a limited, incomplete dark repair of UV-damaged DNA. DNA polymerases I and III thus appear to be important enzymes in both DNA replication and DNA dark repair.