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. It does not contain DNA endonuclease, exonuclease and phosphatase, and does not contain RNA enzyme.