Cytidylyltransferase required for protein O-linked mannosylation (  , ). Catalyzes the formation of CDP-ribitol nucleotide sugar from D-ribitol 5-phosphate ( ). CDP-ribitol is a substrate of FKTN during the biosynthesis of the phosphorylated O-mannosyl trisaccharide (N-acetylgalactosamine-beta-3-N-acetylglucosamine-beta-4-(phosphate-6-)mannose), a carbohydrate structure present in alpha-dystroglycan (DAG1), which is required for binding laminin G-like domain-containing extracellular proteins with high affinity ( ). Shows activity toward other pentose phosphate sugars and mediates formation of CDP-ribulose or CDP-ribose using CTP and ribulose-5-phosphate or ribose-5-phosphate, respectively . Not Involved in dolichol production .
Subcellular locations: Cytoplasm, Cytosol
Ubiquitously expressed, with high expression in brain.