Use Thermo Scientific™ T4 DNA Ligase to catalyze side-by-side 5'-phosphate groups in double helix DNA or RNA and the formation of a phosphodiester bond between the 3'-hydroxyl terminus. The enzyme can repair single-stranded gaps in double-helix DNA, RNA, or DNA/RNA hybrids. It can also ligate DNA fragments via adapters or blunt ends, but is inactive against single-stranded nucleic acids.

T4 DNA ligase requires ATP as a cofactor.