T4 DNA Ligase is isolated and purified from Escherichia coli expressing T4 DNA Ligase gene after induced expression, and can catalyze the phosphodiester bond between the 5 'phosphate group and 3' hydroxyl group of adjacent DNA chains. This enzyme can catalyze the ligation of blunt end or sticky end DNA, repair single-strand cuts in double-stranded DNA, RNA, and single-strand DNA/RNA hybridization, but has no activity for single-stranded nucleotides.