CTP-dependent diacylglycerol kinase that catalyzes the phosphorylation of diacylglycerol (DAG) to phosphatidate (PA). Controls phosphatidate levels at the nuclear envelope. May be involved in vesicle trafficking between the endoplasmic reticulum and the Golgi apparatus. a 1,2-diacyl-sn-glycerol + CTP = a 1,2-diacyl-sn-glycero-3-phosphate + CDP + H(+) Belongs to the DGK1 family.