T4 DNA ligase is a type of DNA ligase. DNA ligase catalyzes the formation of phosphodiester bonds at single-stranded DNA breaks in double-stranded DNA in vivo. DNA ligase has important biological functions in organisms. In DNA repair and recombination, DNA ligase plays a role in connecting gaps. In the process of DNA replication, the synthesis of the lagging strand is discontinuous, and DNA ligase connects the discontinuous DNA strand into a continuous DNA strand. T4 DNA Ligase Ⅱ is a recombinant protein fusion of T4 DNA Ligase and adenylate kinase, The purified T4 DNA Ligase Ⅱ not only is fully active for DNA ligation, but also can use ADP in addition to ATP as energy source since adenylate kinase converts ADP to ATP and AMP. It does not contain DNA endonuclease, exonuclease and phosphatase, and does not contain RNA enzyme.