Phosphatidylserine synthase involved in the regulation of processes such as cell morphology, cytokinesis, actin cytoskeleton, and cell wall remodeling and integrity. Also plays a role in the physiological adaptations required for stationary-phase survival. a CDP-1,2-diacyl-sn-glycerol + L-serine = a 1,2-diacyl-sn-glycero-3-phospho-L-serine + CMP + H(+) Phospholipid metabolism; phosphatidylethanolamine biosynthesis; phosphatidylethanolamine from CDP-diacylglycerol: step 1/2. During log-phase growth, concentrates at the cell and nuclear peripheries as well endoplasmic reticulum membranes, while in stationary-phase cells, is redistributed to unusual cytoplasmic structures of unknown origin. Belongs to the CDP-alcohol phosphatidyltransferase class-I family.