The Drosophila ribosomal protein S3 contains a DNA deoxyribophosphodiesterase (dRpase) activity.

The Drosophila ribosomal protein S3 has been previously demonstrated to cleave DNA containing 8-oxoguanine residues and has also been found to contain an associated apurinic/apyrimidinic (AP) lyase activity that 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 was found to efficiently remove sugar-phosphate residues from DNA substrates containing 5'-incised AP sites as well as from DNA substrates containing 3'-incised sites. Removal of 2-deoxyribose-5-phosphate as 4-hydroxy-2-pentenal-5-phosphate from a substrate containing 5'-incised AP sites occurred via a beta-elimination reaction, as indicated by reaction of the released sugar-phosphate products with sodium thioglycolate. The reaction for the removal of 4-hydroxy-2-pentenal-5-phosphate from the substrate containing 3'-incised AP sites was dependent on the presence of the Mg2+ cation. These findings suggest that the S3 ribosomal protein may function in several steps of the DNA base excision repair pathway in eukaryotes and may represent an important DNA repair function for the repair of oxidative and ionizing radiation-induced DNA damage.