Comparison of functional properties of mammalian DNA polymerase λ and DNA polymerase β in reactions of DNA synthesis related to DNA repair

DNA polymerase λ (Pol λ) is a novel enzyme of the family X of DNA polymerases. Pol λ has some properties in common with DNA polymerase β (Pol β). The substrate properties of Pol λ were compared to Pol β using DNAs mimicking short-patch (SP) and long-patch (LP) base excision repair (BER) intermediates as well as recessed template primers. In the present work, the influence of several BER proteins such as flap-endonuclease-1 (FEN1), PCNA, and apurinic/apyrimidinic endonuclease-1 (APE1) on the activity of Pol λ was investigated. Pol λ is unable to catalyze strand displacement synthesis using nicked DNA, although this enzyme efficiently incorporates a dNMP into a one-nucleotide gap. FEN1 and PCNA stimulate the strand displacement activity of Pol λ. FEN1 processes nicked DNA, thus removing a barrier to Pol λ DNA synthesis. It results in a one-nucleotide gapped DNA molecule that is a favorite substrate of Pol λ. Photocrosslinking and functional assay show that Pol λ is less efficient than Pol β in binding to nicked DNA. APE1 has no influence on the strand displacement activity of Pol λ though it stimulates strand displacement synthesis catalyzed with Pol β. It is suggested that Pol λ plays a role in the SP BER rather than contributes to the LP BER pathway.