Evidence implying DNA polymerase beta function in excision repair.

Comparison was made of the ability of calf thymus DNA polymerases alpha and beta to replicate the following templates: native E. coli CR-34 DNA (T-DNA), calf thymus DNA activated by DNase I (act.DNA), BU-DNA (from E. coli CR-34 cells cultured on BUdR-containing medium) with damages resulting from incomplete excision repair, as well as thermally denatured act.DNA and BU-DNA (s.s.act.DNA and s.s.BU-DNA). 3H-TTP incorporation during extensive replication of act.DNA was similar for both enzymes, being, as expected, 40 times higher than for T-DNA. Likewise, the differences in the yield of the s.s.act.DNA or s.s.BU-DNA replication between both enzymes were negligible. In contrast, damaged native DNA was 6 - 30 times more extensively replicated by DNA polymerase beta than alpha. We propose that this is due to the greater ability of DNA polymerase beta compared with alpha to replicate single-stranded gaps, the presence of which is more likely in damaged BU-DNA than in T-DNA and act.DNA.