DNA ligase that seals nicks in double-stranded DNA during DNA replication, DNA recombination and DNA repair. Shows high activity with either ATP or NAD(+). ATP + (deoxyribonucleotide)n-3'-hydroxyl + 5'-phospho-(deoxyribonucleotide)m = (deoxyribonucleotide)n+m + AMP + diphosphate. NAD(+) + (deoxyribonucleotide)n-3'-hydroxyl + 5'-phospho-(deoxyribonucleotide)m = (deoxyribonucleotide)n+m + AMP + beta-nicotinamide D-nucleotide. Optimum pH is 7.0. Optimum temperature is 65 degrees Celsius. Loses half of its activity in 15 min at 90 degrees Celsius. Belongs to the ATP-dependent DNA ligase family.