Catalyzes the terminal and only committed step in triacylglycerol synthesis by using diacylglycerol and fatty acyl CoA as substrates. Required for storage lipid synthesis (Probable). Upon expression in E.coli functions as a triacylglycerol synthase, making triacylglycerol (TG) from diolein and long-chain fatty acyl-CoA. Prefers C(26:0)-CoA over C(18:1)-CoA. TG synthesis activity increases in M.tuberculosis upon oxygen depletion and NO treatment, with concomitant accumulation of TG in inclusion bodies. As disruption of the gene encoding this protein obviates TG synthesis this seems to be the major enzyme involved in production of TG. Has no wax synthase activity to produce wax esters. a 1,2-diacyl-sn-glycerol + an acyl-CoA = a triacyl-sn-glycerol + CoA (9Z)-octadecenoyl-CoA + di-(9Z)-octadecenoylglycerol = 1,2,3-tri-(9Z-octadecenoyl)-glycerol + CoA Upon expression in E.coli. Optimum pH is 4.5. Glycerolipid metabolism; triacylglycerol biosynthesis. A member of the dormancy regulon. Induced in response to reduced oxygen tension (hypoxia), low levels of nitric oxide (NO) and carbon monoxide (CO). It is hoped that this regulon will give insight into the latent, or dormant phase of infection. Also induced when grown at pH 5.0 for 3 weeks. No detectable TG under hypoxic growth conditions, or when grown at pH 5.0. However, about 30% of normal levels of TG accumulated when grown in the presence of NO but there was virtually no C(26:0) TG produced. Belongs to the long-chain O-acyltransferase family.