enzymes that catalyse the ligation of two molecules with concomitant hydrolysis of the pyrophosphate bond in adenosine 5'-triphosphate (ATP) or a similar triphosphate, forming C–C, C–O, C–S, P–O or C–N bonds. In recombinant DNA technology, ligases covalently join together two sequences of DNA (e.g. host DNA and foreign DNA) by a phosphodiester bond.