Human DNA polymerase λ possesses terminal deoxyribonucleotidyl transferase activity and can elongate RNA primers: Implications for novel functions

DNA polymerase λ is a novel enzyme of the family X of DNA polymerases. The recent demonstration of an intrinsic 5′-deoxyribose-5′-phosphate lyase activity, a template/primer dependent polymerase activity, a distributive manner of DNA synthesis and sequence similarity to DNA polymerase β suggested a novel β-like enzyme. All these properties support a role of DNA polymerase λ in base excision repair. On the other hand, the biochemical properties of the polymerisation activity of DNA polymerase λ are still largely unknown. Here we give evidence that human DNA polymerase λ has an intrinsic terminal deoxyribonucleotidyl transferase activity that preferentially adds pyrimidines onto 3′OH ends of DNA oligonucleotides. Furthermore, human DNA polymerase λ efficiently elongates an RNA primer hybridized to a DNA template. These two novel properties of human DNA polymerase λ might suggest additional roles for this enzyme in DNA replication and repair processes.