Able to ligate a double-stranded synthetic DNA substrate containing a single nick and inefficiently ligated a 1 nucleotide gap but did not ligate a 2 nucleotide gap. It is able to ligate short, complementary overhangs but not blunt-ended double-stranded DNA. May be implicated in DNA repair and recombination. ATP + (deoxyribonucleotide)n-3'-hydroxyl + 5'-phospho-(deoxyribonucleotide)m = (deoxyribonucleotide)n+m + AMP + diphosphate. Belongs to the ATP-dependent DNA ligase family.