APE1 is the major 3'-phosphoglycolate activity in human cell extracts

DNA strand breaks containing 3′-phosphoglycolate (3′-PG) ends are the major lesions induced by ionizing radiation. The repair of this lesion is not completely understood and several activities are thought to be involved in processing of 3′-PG ends. In this study we examined activities in human whole cell extracts (WCE) responsible for removal of 3′-PG. Using a radiolabelled oligonucleotide containing a single nucleotide gap with internal 5′-phosphate and 3′-PG ends, we demonstrate that the major 3′-PG activity in human WCE is Mg²⁺ dependent and that this activity co-purifies with AP endonuclease 1 (APE1) over phosphocellulose and gel filtration chromatography. Furthermore, immunodepletion of APE1 from active gel filtration fractions using APE1 specific antibodies reveals that the major activity against 3′-PG in human WCE is APE1.