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

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 Iyase) activity of DNA polymerase beta (Pol beta). DNA polymerase lambda (Pol lambda) is a recently identified eukaryotic DNA polymerase that is homologous to Pol beta. We show here that human Pol lambda exhibits dRP, lyase, but not AP lyase, activity in vitro and that this activity is consistent with a beta -elimination mechanism. Accordingly, a single amino acid substitution (K310A) eliminated more than 90% of the wild-type dRP lyase activity, thus suggesting that LyS(310) of Pol lambda is the main nucleophile involved in the reaction. The dRP lyase activity of Pol A, in coordination with its polymerization activity, efficiently repaired uracil-containing DNA in an in vitro reconstituted BER reaction. These results suggest that Pol lambda may participate in "single-nucleotide" base excision repair in mammalian cells.