Yeast DNA 3'-repair diesterase is the major cellular apurinic/apyrimidinic endonuclease: substrate specificity and kinetics

DNA strand breaks with damaged 3' termini are potentially toxic lesions caused by free radicals. The purified yeast diesterase that removes small nucleotide fragments from such 3' termini in oxidized DNA has been further characterized with respect to its substrate specificity. In addition to the 3'-phosphoglycolaldehyde esters used to monitor the activity during purification, the enzyme efficiently hydrolyzed a variety of other 3'-esters in DNA. These included 3'-phosphates, 3'-(2,3-didehydro-2,3-dideoxyribose phosphates), and the 3'-blocking damages formed in vivo in Escherichia coli by H2O2 or in vitro by DNA treatment with bleomycin. This same transition metal-dependent enzyme also constitutes the major yeast endonuclease for apurinic/apyrimidinic sites in DNA, hydrolyzing these damages to yield normal 3'-hydroxyl nucleotides and 5'-phosphoryl base-free sugar termini (a Type II apurinic/apyrimidinic endonuclease). Yeast 3'-phosphoglycolaldehyde diesterase therefore appears to be involved in two distinct pathways of DNA repair: initiation of the repair of oxidative strand breaks in DNA and the restoration of sites of base loss caused by many types of DNA-damaging agents.