YEAST STRUCTURAL GENE (APN1) FOR THE MAJOR APURINIC ENDONUCLEASE - HOMOLOGY TO ESCHERICHIA-COLI ENDONUCLEASE-IV

DNA damage generated by oxygen radicals des base-free apurinic/apyrimidinic (AP) sites and strand breaks that bear deoxyribose fragments. The yeast Saccharoces cerevisiae repairs such DNA lesions by using a single major enzyme. We have cloned the yeast structural gene (APN1) encoding this AP endonuclease/3′-repair diesterase by Immunological screening of a yeast genomic DNA expression library in λgt11. Gene disruption experiments confirm that the Aga1 protein accounts for >97% of both AP endonuclease and DNA 3′-repair diesterase activities in yeast cell-free extracts. The DNA and predicted amino acid sequences for the APN1 gene are homologous to those for the nfo gene encoding DNA endonuclease IV of Escherichia coli. This conservation of structure between a eukaryotic enzyme and its prokaryotic counterpart underscores the fundamental nature of their roles in DNA repair.