DNA ligase, which is expressed in the early stage of lytic development, has been implicated in T7 DNA synthesis and genetic recombination. It may also play a role in T7 DNA repair. ATP + (deoxyribonucleotide)n-3'-hydroxyl + 5'-phospho-(deoxyribonucleotide)m = (deoxyribonucleotide)n+m + AMP + diphosphate. Belongs to the ATP-dependent DNA ligase family.