Micrococcus luteus endonucleases for apurinic/apyrimidinic sites in deoxyribonucleic acid. 2. Further studies on the substrate specificity and mechanism of action.

Two endonucleases specific for DNA-containing apurinic or apyrimidinic sites (AP-endonucleases A and B) have been isolated from Micrococcus luteus and highly purified. These enzymes have no exonuclease activity. Both AP-endonucleases hydrolyze DNA-containing apurinic or apyrimidinic sites at the 5' end of the lesion, thus generating 3'-hydroxyl and 5'-phosphoryl end groups. DNA-containing pyrimidine dimers, introduced at low doses of UV, are not hydrolyzed, whereas DNA-containing lesions, introduced at high doses of UV or by gamma irradiation are nicked by either AP-endonuclease. During hydrolysis of apurinic DNA, neither of the AP-endonucleases acts as a processive enzyme.