MAMMALIAN DNA-LIGASE II IS HIGHLY HOMOLOGOUS WITH VACCINIA DNA-LIGASE- IDENTIFICATION OF THE DNA-LIGASE-II ACTIVE-SITE FOR ENZYME-ADENYLATE FORMATION

Mammalian cells contain three biochemically distinct DNA ligases. In t his report we describe the purification of DNA ligase II to homogeneit y from bovine liver nuclei. This enzyme interacts with ATP to form an enzyme-AMP complex, in which the AMP moiety is covalently linked to a lysine residue. An adenylylated peptide from DNA ligase II contains th e sequence, Lys-Tyr-Asp-Gly-Glu-Arg, which is homologous to the active site motif conserved in ATP-dependent DNA ligases, The sequences adja cent to this motif in DNA ligase II are different from the comparable sequences in DNA ligase I, demonstrating that these enzymes are encode d by separate genes. The amino acid sequences of 15 DNA ligase II pept ides exhibit striking homology (65% overall identity) with vaccinia DN A ligase. These peptides are also homologous (31% overall identity) wi th the catalytic domain of mammalian DNA ligase I, indicating that the genes encoding DNA ligases I and II probably evolved from a common an cestral gene. Since vaccinia DNA ligase is not required for DNA replic ation but influences the ability of the virus to survive DNA damage, t he homology between this enzyme and DNA ligase II suggests that DNA li gase II may be involved in DNA repair.