Abstract
A protein factor having exonucleolytic activity on bleomycindamaged DNA and providing priming sites for DNA polymerasesexisted in a DNA polymerase β fraction partially purified by ion exchange chromatography from an extract of permeable mouse ascites sarcoma (SR-C3H/He) cells. The exonuclease was separated from DNA polymerase β by singlestranded DNA-cellulose chromatography, and partially characterized. The enzyme is suggestedto be involved in the initial step of repair of bleomycin-damaged DNA in removing 3′ ends (3′-phosphoglycolate termini) of bleomycin-damaged DNA.