Catalyzes the phosphorylation of diacylglycerol (DAG) into phosphatidic acid. Is involved in the biosynthesis of phosphatidylinositol mannosides (PIMs), probably via a role in the biosynthesis of phosphatidylinositol (PI), a PIM precursor, which is derived from phosphatidic acid. a 1,2-diacyl-sn-glycerol + ATP = a 1,2-diacyl-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. Belongs to the diacylglycerol/lipid kinase family.