T4 DNA Ligase is a ligation enzyme that can be used to join DNA fragments by catalyzing the formation of phosphodiester bonds between juxtaposed 5' phosphate and 3' hydroxyl termini in double-stranded DNA using ATP as a coenzyme. Both blunt and cohesive end DNA ligation, as well as single-stranded nick repair of DNA, RNA and DNA/RNA, are possible using the T4 DNA ligase.