Upon expression in E.coli functions very weakly as a triacylglycerol synthase, making triacylglycerol (TG) from diolein and long-chain fatty acyl-CoA. Has no wax synthase activity. a 1,2-diacyl-sn-glycerol + an acyl-CoA = a triacyl-sn-glycerol + CoA Glycerolipid metabolism; triacylglycerol biosynthesis. Constitutively expressed at a low level, it is not further induced by hypoxia or nitric oxide exposure. Belongs to the long-chain O-acyltransferase family.