Required for CpsD phosphorylation. Involved in the regulation of capsular polysaccharide biosynthesis. May be part of a complex that directs the coordinated polymerization and export to the cell surface of the capsular polysaccharide (By similarity). Capsule biogenesis; capsule polysaccharide biosynthesis. Belongs to the CpsC/CapA family. Was originally called CpsB.