Component of the Rcs signaling system, which controls transcription of numerous genes. RcsD is a phosphotransfer intermediate between the sensor kinase RcsC and the response regulator RcsB. It acquires a phosphoryl group from RcsC and transfers it to RcsB. The system controls expression of genes involved in colanic acid capsule synthesis, biofilm formation and cell division. Interacts with RcsC and RcsB. Has a higher affinity for RcsB than for RcsC. Phosphorylated by RcsC. Belongs to the RcsD family. Contains a histidine kinase domain, but it seems to be non-functional as the highly conserved histidine residue is missing.