- The DNA repair endonuclease XPG binds to proliferating cell nuclear antigen (PCNA) and shares sequence elements with the PCNA-binding regions of FEN-1 and cyclin-dependent kinase inhibitor p21. Gary, R., Ludwig, D.L., Cornelius, H.L., MacInnes, M.A., Park, M.S. J. Biol. Chem. (1997)