Catalyzes the phosphorylation of diacylglycerol (DAG) into phosphatidic acid. Is a key enzyme involved in the production of lipoteichoic acid by reintroducing DAG formed from the breakdown of membrane phospholipids into the phosphatidylglycerol biosynthetic pathway. Is more active toward long-chain DAG compared with short-chain DAG. Is not able to phosphorylate substrates other than DAG, such as monoacylglycerol, ceramide, undecaprenol, phosphatidylinositol, or sphingosine. a 1,2-diacyl-sn-glycerol + ATP = a 1,2-diacyl-sn-glycero-3-phosphate + ADP + H(+) 1,2-di-(9Z-octadecenoyl)-sn-glycerol + ATP = 1,2-di-(9Z-octadecenoyl)-sn-glycero-3-phosphate + ADP + H(+) Binds 1 Mg(2+) ion per subunit. This ion appears to have a structural role and is required for catalytic activity. Cells lacking this gene are not viable. They exhibit accumulation of diacylglycerol, disappearance of phosphatidylglycerol, and the cessation of lipoteichoic acid formation. Belongs to the diacylglycerol/lipid kinase family.