Essential acyltransferase that catalyzes the terminal and only committed step in triacylglycerol synthesis by using diacylglycerol and fatty acyl CoA as substrates. Required for synthesis and storage of intracellular triglycerides. Probably plays a central role in cytosolic lipid accumulation (By similarity). a 1,2-diacyl-sn-glycerol + an acyl-CoA = a triacyl-sn-glycerol + CoA all-trans-retinol + an acyl-CoA = an all-trans-retinyl ester + CoA (9Z)-octadecenoyl-CoA + 2-(9Z-octadecenoyl)-glycerol = 1,2-di-(9Z-octadecenoyl)-sn-glycerol + CoA (9Z)-octadecenoyl-CoA + 1,2-di-(9Z-octadecenoyl)-sn-glycerol = 1,2,3-tri-(9Z-octadecenoyl)-glycerol + CoA all-trans-retinol + hexadecanoyl-CoA = all-trans-retinyl hexadecanoate + CoA (9Z)-octadecenoyl-CoA + 1-O-(9Z-octadecenyl)-glycerol = 1-O-(9Z-octadecenyl)-mono-(9Z-octadecenoyl)-glycerol + CoA (9Z)-octadecenoyl-CoA + 1-(9Z-octadecenoyl)-glycerol = 1,2-di-(9Z-octadecenoyl)-glycerol + CoA 1,2-di-(9Z-octadecenoyl)-sn-glycerol + hexadecanoyl-CoA = 1,2-di-(9Z)-octadecenoyl-3-hexadecanoyl-sn-glycerol + CoA (9Z)-octadecenoyl-CoA + 1,3-di-(9Z-octadecenoyl)-glycerol = 1,2,3-tri-(9Z-octadecenoyl)-glycerol + CoA (9Z)-octadecenoyl-CoA + 2,3-di-(9Z)-octadecenoyl-sn-glycerol = 1,2,3-tri-(9Z-octadecenoyl)-glycerol + CoA 2-(9Z-octadecenoyl)-glycerol + hexadecanoyl-CoA = 1-hexadecanoyl-2-(9Z-octadecenoyl)-sn-glycerol + CoA Glycerolipid metabolism; triacylglycerol biosynthesis. Belongs to the diacylglycerol acyltransferase family.