THE YEAST 8-OXOGUANINE DNA GLYCOSYLASE (OGG1) CONTAINS A DNA DEOXYRIBOPHOSPHODIESTERASE (DRPASE) ACTIVITY

The yeast OGG1 gene was recently cloned and shown to encode a protein that possesses N-glycosylase/AP lyase activities for the repair of oxi datively damaged DNA at sites of 7, 8-dihydro-8-oxoguanine (8-oxoguani ne). Similar activities have been identified for Escherichia coli form amidopyrimidine-DNA glycosylase (Fpg) and Drosophila ribosomal protein S3. Both Fpg and S3 also contain a deoxyribophosphodiesterase (dRpase ) activity. that removes 2-deoxyribose-5-phosphate at an incised 5' ap urinic/apyrimidinic (AP) sites via a beta-elimination reaction. Drosop hila S3 also has an additional activity that removes trans-4-hydroxy-2 -pentenal-5-phosphate at a 3' incised AP site by a Mg2+-dependent hydr olytic mechanism, In view of the substrate similarities between Ogg1, Fpg and S3 at the level of base excision repair, we examined whether O gg1 also contains dRpase activities. A glutathione S-transferase fusio n protein of Ogg1 was purified and subsequently found to efficiently r emove sugar-phosphate residues at incised 5' AP sites. Activity was al so detected for the Mg2+-dependent removal of trans-4-hydroxy-2-penten al-5-phosphate at 3' incised AP sites and from intact AP sites. Previo us studies have shown that DNA repair proteins that possess AP lyase a ctivity leave an inefficient DNA terminus for subsequent DNA synthesis steps associated with base excision repair. However, the results pres ented here suggest that in the presence of MgCl2, Ogg1 can efficiently process 8-oxoguanine so as to leave a one nucleotide gap that can be readily filled in by a DNA polymerase, and importantly, does not there fore require additional enzymes to process trans-4-hydroxy-2-pentenal- 5-phosphate left at a 3' terminus created by a p-elimination catalyst.