Escherichia coli RcsA, a Positive Activator of Colanic Acid Capsular Polysaccharide Synthesis, Functions To Activate Its Own Expression

Capsule (cps) gene expression in Escherichia coli is controlled by a complex network of regulators. Transcription of the cps operon is controlled by at least two positive regulators, RcsA and RcsB. We show here that RcsA functions to activate its own expression, as seen by the 100-fold-increased expression of a rcsA::lacZ transcriptional fusion in strains with high levels of RcsA protein, either due to a mutation in lon or due to overexpression of RcsA from a multicopy plasmid. Expression of the rcsA::lacZ fusion is increased by but not dependent on the presence of RcsB. In addition, the effects of H-NS and RcsB on the expression of rcsA are independent of each other. A sequence motif, conserved between the E. coli cps promoter and the Erwinia amylovora ams promoter and previously shown to be the RcsA-RcsB binding site, was identified in the rcsA promoter region and shown to be required for high-level expression of rcsA.