from David J. Clarke writing in Two-Component Systems in Bacteria:
The Rcs phosphorelay is a complex signaling network that is restricted in distribution to the Enterobacteriaceae. The core Rcs phosphorelay is composed of 3 proteins: the sensor kinase RcsC, the HPt domain protein RcsD and the response regulator RcsB. In addition to these core components the Rcs phosphorelay also contains some auxiliary proteins that are involved in mediating the inputs to and outputs from this signaling pathway. Therefore RcsF is a lipoprotein involved in signal perception, IgaA inhibits the activity of the phosphorelay and RcsA is required for the expression of some of the genes that are regulated by the phosphorelay. Whilst initially identified as a positive regulator of capsule production in Escherichia coli the Rcs phosphorelay is now recognized as a key regulator of motility, biofilm formation and virulence in many members of the Enterobacteriaceae.
Further reading: Two-Component Systems in Bacteria