Mutation of the cognate response regulator gene rcsB restored full virulence to the rcsC constitutive mutant , indicating that virulence attenuation results from aberrant expression of RcsB-regulated genes.The virulence attenuation phenotype was partially dependent on the regulatory gene rcsA , which is necessary for transcription of certain RcsB-regulated genes , and on the RcsB-and RcsA-dependent colanic acid capsule synthesis cps operon .