Involved in triacylglycerol (TAG) synthesis. Catalyzes the acylation of the sn-3 hydroxy group of sn-1,2-diacylglycerol using acyl-CoA. a 1,2-diacyl-sn-glycerol + an acyl-CoA = a triacyl-sn-glycerol + CoA Glycerolipid metabolism; triacylglycerol biosynthesis. Belongs to the membrane-bound acyltransferase family. Sterol o-acyltransferase subfamily.