DNA binding activity from cultured human fibrolasts that is specific for partially depurinated DNA and that inserts purines into apurinic sites.

Abstract

A protein of MW .apprxeq. 120,000 was isolated from cultured human fibroblasts and HeLa [human cervical cancer] cells on the basis of its ability to bind specifically to apurinic DNA. After separation from apurinic endonuclease activity, the protein incorporated purine but not pyrmidine bases specifically into depurinated DNA to protect the apurinic sites from alkali. Purine base insertion activity was sensitive to heating and freezing and to caffeine and EDTA. It required K+ but not a divalent cation. Guanine but not adenine was incorporated into depurinated poly(dG-dC), but adenine, not guanine, was incorporated into poly(dA-dT). After incorporation into depurinated DNA, guanine could be reisolated as dGMP. Although this activity suggests an alternative pathway for DNA repair that is independent of nucleotide excision, other functions for such an enzyme are possible.