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-postiabeling 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 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.
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