Catalyzes the conversion of phosphatidic acid (PA) to CDP-diacylglycerol (CDP-DAG), an essential intermediate in the synthesis of phosphatidylglycerol, cardiolipin and phosphatidylinositol (PubMed:9407135, PubMed:25375833). Exhibits almost no acyl chain preference for PA, showing no discrimination for the sn-1/sn-2 acyl chain composition of PAs (PubMed:25375833). Plays an important role in regulating the growth of lipid droplets which are storage organelles at the center of lipid and energy homeostasis (PubMed:26946540, PubMed:31548309). Positively regulates the differentiation and development of adipocytes (By similarity). a 1,2-diacyl-sn-glycero-3-phosphate + CTP + H(+) = a CDP-1,2-diacyl-sn-glycerol + diphosphate 1-octadecanoyl-2-(5Z,8Z,11Z,14Z-eicosatetraenoyl)-sn-glycero-3-phosphate + CTP + H(+) = 1-octadecanoyl-2-(5Z,8Z,11Z,14Z-eicosatetraenoyl)-sn-glycero-3-cytidine-5'-diphosphate + diphosphate 1-octadecanoyl-2-(9Z,12Z-octadecadienoyl)-sn-glycero-3-phosphate + CTP + H(+) = 1-octadecanoyl-2-(9Z,12Z-octadecadienoyl)-sn-glycero-3-cytidine-5'-diphosphate + diphosphate 1-hexadecanoyl-2-(5Z,8Z,11Z,14Z-eicosatetraenoyl)-sn-glycero-3-phosphate + CTP + H(+) = 1-hexadecanoyl-2-(5Z,8Z,11Z,14Z-eicosatetraenoyl)-sn-glycero-3-cytidine-5'-diphosphate + diphosphate 1,2-di-(5Z,8Z,11Z,14Z)-eicosatetraenoyl-sn-glycero-3-phosphate + CTP + H(+) = 1,2-di-(5Z,8Z,11Z,14Z-eicosatetraenoyl)-sn-glycero-3-cytidine-5'-diphosphate + diphosphate 1-octadecanoyl-2-(9Z-octadecenoyl)-sn-glycero-3-phosphate + CTP + H(+) = 1-octadecanoyl-2-(9Z-octadecenoyl)-sn-glycero-3-cytidine-5'-diphosphate + diphosphate 1-octadecanoyl-2-(4Z,7Z,10Z,13Z,16Z,19Z-docosahexaenoyl)-sn-glycero-3-phosphate + CTP + H(+) = 1-octadecanoyl-2-(4Z,7Z,10Z,13Z,16Z,19Z-docosahexaenoyl)-sn-glycero-3-cytidine-5'-diphosphate + diphosphate 1,2-di-(9Z,12Z-octadecadienoyl)-sn-glycero-3-phosphate + CTP + H(+) = 1,2-di-(9Z,12Z-octadecadienoyl)-sn-glycero-3-cytidine-5'-diphosphate + diphosphate 1,2-di-(9Z-octadecenoyl)-sn-glycero-3-phosphate + CTP + H(+) = 1,2-di-(9Z-octadecenoyl)-sn-glycero-3-cytidine-5'-diphosphate + diphosphate Inhibited by its anionic phospholipid end products, with phosphatidylinositol-(4,5)- bisphosphate showing the strongest inhibition. Phospholipid metabolism; CDP-diacylglycerol biosynthesis; CDP-diacylglycerol from sn-glycerol 3-phosphate: step 3/3. Homodimer (By similarity). Interacts with FOS; this interaction may enhance catalytic activity (By similarity). Expressed in adult tissues such as placenta, brain, small intestine, ovary, testis and prostate. Highly expressed in fetal kidney, lung and brain. Lower level in fetal liver. Belongs to the CDS family.