Enables phosphatidate cytidylyltransferase activity. Predicted to be involved in glycerophospholipid biosynthetic process; lipid droplet formation; and positive regulation of fat cell differentiation. Located in endoplasmic reticulum membrane. Is integral component of membrane. Orthologous to human CDS1 (CDP-diacylglycerol synthase 1). [provided by Alliance of Genome Resources, Apr 2022]