DNA ligase that seals nicks in double-stranded DNA during DNA replication, DNA recombination and DNA repair. ATP + (deoxyribonucleotide)n-3'-hydroxyl + 5'-phospho-(deoxyribonucleotide)m = (deoxyribonucleotide)n+m + AMP + diphosphate. Optimum temperature is about 70 degrees Celsius. Active from 4 to 100 degrees Celsius. Thermostable. Monomer. Belongs to the ATP-dependent DNA ligase family.