Identification of an intrinsic 5′-deoxyribose-5-phosphate lyase activity in human DNA polymerase λ: A possible role in base excision repair

Abstract

Base excision repair (BER) is a major repair pathway in eukaryotic cells responsible for repair of lesions that give rise to abasic (AP) sites in DNA. Pivotal to this process is the 5′-deoxyribose-5-phosphate lyase (dRP lyase) activity of DNA polymerase β (Pol β). DNA polymerase λ (Pol λ) is a recently identified eukaryotic DNA polymerase that is homologous to Pol β. We show here that human Pol λ exhibits dRP lyase, but not AP lyase, activity in vitro and that this activity is consistent with a β-elimination mechanism. Accordingly, a single amino acid substitution (K310A) eliminated more than 90% of the wild-type dRP lyase activity, thus suggesting that Lys310 of Pol λ is the main nucleophile involved in the reaction. The dRP lyase activity of Pol λ, in coordination with its polymerization activity, efficiently repaired uracil-containing DNA in an in vitro reconstituted BER reaction. These results suggest that Pol λ may participate in "single-nucleotide" base excision repair in mammalian cells.