DNA ligase that seals nicks in double-stranded DNA during DNA replication, DNA recombination and DNA repair. Can use ATP, ADP and GTP, but not CTP, TTP or NAD(+). ATP + (deoxyribonucleotide)n-3'-hydroxyl + 5'-phospho-(deoxyribonucleotide)m = (deoxyribonucleotide)n+m + AMP + diphosphate. ADP + (deoxyribonucleotide)n-3'-hydroxyl + 5'-phospho-(deoxyribonucleotide)m = (deoxyribonucleotide)n+m + AMP + phosphate. GTP + (deoxyribonucleotide)n-3'-hydroxyl + 5'-phospho-(deoxyribonucleotide)m = (deoxyribonucleotide)n+m + GMP + diphosphate. Other divalent cations such as Zn(2+), Ni(2+), Ca(2+) and Co(2+) are not able to activate the enzyme. Optimum pH is 7.0. Optimum temperature is 75 degrees Celsius. Activity declines drastically at temperatures from 75 to 80 degrees Celsius. Belongs to the ATP-dependent DNA ligase family.