lyase APE1 AP endonuclease 1 APEN APEX nuclease DNA-(apurinic or apyrimidinic site) lyase DNA-(apurinic or apyrimidinic site) lyase (EC 4.2.99.18) (AP endonuclease 1) (APEX nuclease) (APEN) (REF-1 protein) EC:4.2.99.18 IMR:0010142 REF-1 protein molecule_role