Human HeLa cell enzymes that remove phosphoglycolate 3'-end groups from DNA.

We have purified three chromatographically distinct human enzyme activities from HeLa cells, that are capable of converting bleomycin-treated DNA into a substrate for E. coli DNA polymerase I. The bleomycin-treated DNA substrate used in this study has been characterized via a 32P-postlabeling assay and shown to contain strand breaks with 3'-phosphoglycolate termini as greater than 95% of the detectable dose-dependent lesions. The purified HeLa cell enzymes were shown to be capable of removing 3'-phosphoglycolates from this substrate. Also 3'-phosphoglycolate removal and nucleotide incorporation were enzyme dependent. In addition, all three Hela cell enzymes have been determined to possess Class II AP endonuclease activity. The enzymes lack 3'----5' exonuclease activity and are, therefore, dissimilar to exonuclease III--an E. coli enzyme that can remove 3'-phosphoglycolate.