THE DROSOPHILA RIBOSOMAL-PROTEIN S3 CONTAINS A DNA DEOXYRIBOPHOSPHODIESTERASE (DRPASE) ACTIVITY

The Drosophila ribosomal protein S3 has been previously demonstrated t o cleave DNA containing 8-oxoguanine residues and has also been found to contain an associated apurinic/apyrimidinic (AP) lyase activity tha t cleaves phosphodiester bonds via a beta, delta-elimination reaction. The activity of this protein on DNA substrates containing incised AP sites was examined. A glutathione S-transferase fusion protein of S3 w as found to efficiently remove sugar-phosphate residues from DNA subst rates containing 5'-incised AP sites as well as from DNA substrates co ntaining 3'-incised sites. Removal of 2-deoxyribose-5-phosphate as 4-h ydroxy-2-pentenal-5-phosphate from a substrate containing 5'-incised A P sites occurred via a beta-elimination reaction, as indicated by reac tion of the released sugar-phosphate products with sodium thioglycolat e. The reaction for the removal of 4-hydroxy-2-pentenal-5-phosphate fr om the substrate containing 3'-incised AP sites was dependent oil the presence of the Mg2+ cation. These findings suggest that the S3 riboso mal protein may function in several steps of the DNA base excision rep air pathway in eukaryotes and may represent an important DNA repair fu nction for the repair of oxidative and ionizing radiation-induced DNA damage.