Cytidylyltransferase-like domain. Many of these proteins are known to use CTP or ATP and release pyrophosphate. Protein families that contain at least one copy of this domain include citrate lyase ligase, pantoate-beta-alanine ligase, glycerol-3-phosphate cytidyltransferase, ADP-heptose synthase, phosphocholine cytidylyltransferase, lipopolysaccharide core biosynthesis protein KdtB, the bifunctional protein NadR, and a number whose function is unknown.