ligases (synthetases) 

https://doi.org/10.1351/goldbook.L03521
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.
Source:
PAC, 1992, 64, 143. (Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)) on page 159 [Terms] [Paper]