PARTIAL-PURIFICATION OF PDE1 FROM SACCHAROMYCES-CEREVISIAE - ENZYMATIC REDUNDANCY FOR THE REPAIR OF 3'-TERMINAL DNA LESIONS AND ABASIC SITES IN YEAST

Earlier work indicates that the major DNA repair phosphodiesterase (PD E) in yeast cells is the well-characterized Apn1 protein. Apn1 demonst rates both Mg2+-independent PDE activity and Mg2+ independent class II apurinic/apyrimidinic (AP) endonuclease activity and represents great er than 90% of the activity detected in crude extracts from wild-type yeast cells. Apn1 is related to Echerichia coli endonuclease IV, both in its enzymatic properties and its amino acid sequence. In this work, we report the partial purification of a novel yeast protein, Pde1, pr esent in Apn1-deficient cells. Pde1 is purified by sequential BioRex-7 0, PBE118, and MonoS chromatography steps using a sensitive and highly specific 3'-phosphoglycolate-terminated oligonucleotide-based assay a s a measure of PDE activity. Mg2+-stimulated PDE and Mg2+-stimulated c lass II AP endonuclease copurify during this procedure. These results indicate that yeast, like many other organisms studied to date, has en zymatic redundancy for the repair of 3'-blocking groups and abasic sit es.