A Mammalian Endonuclease Specific for Apurinic Sites in Double-stranded Deoxyribonucleic Acid

Abstract

Abstract An endonuclease that attacks double stranded DNA, into which apurinic sites have been introduced previously, has been purified 830-fold from calf thymus cell extracts. The nuclease has a pH optimum at 8.5, is strongly stimulated by the presence of Mg2+ or Mn2+, and has a molecular weight of 32,000 ± 3,000. In double stranded circular DNA molecules containing a small number of apurinic sites, 0.9 to 1.0 chain scission per site is introduced by the enzyme. The enzyme catalyzes the formation of single strand breaks in DNA, adjacent to the apurinic sites. It does not attack native DNA, alkali-denatured DNA, single-stranded DNA containing apurinic sites, or RNA. Enzymatic incisions are apparently introduced at the 3' side of apurinic residues in DNA.