DNA polymerase λ from calf thymus preferentially replicates damaged DNA

A new gene (POLL), has been identified encoding the novel DNA polymerase λ and mapped to mouse chromosome 19 and at human chromosome 10. DNA polymerase λ contains all the critical residues involved in DNA binding, nucleotide binding, nucleotide selection, and catalysis of DNA polymerization and has been assigned to family X based on sequence homology with polymerase β, λ, μ, and terminal deoxynucleotidyltransferase. Here we describe a purification of DNA polymerase λ from calf thymus that preferentially can replicate damaged DNA. By testing polymerase activity on non-damaged and damaged DNA, DNA polymerase λ was purified trough five chromatographic steps to near homogeneity and identified as a 67-kDa polypeptide that cross-reacted with monoclonal antibodies against DNA polymerase β and polyclonal antibodies against DNA polymerase λ. DNA polymerase λ had no detectable nuclease activities and, in contrast to DNA polymerase β, was aphidicolin-sensitive. DNA polymerase λ was a 6-fold more accurate enzyme in an M13mp2 forward mutation assay and 5-fold more accurate in an M13mp2T90 reversion system than human recombinant DNA polymerase β. The biochemical properties of the calf thymus DNA polymerase λ, described here for the first time, are discussed in relationship to the proposed role for this DNA polymerase in vivo.