EXPRESSION OF THE TOLQRA GENES OF ESCHERICHIA-COLI K-12 IS CONTROLLEDBY THE RCSC SENSOR PROTEIN INVOLVED IN CAPSULE SYNTHESIS

The tolQRABpal cluster of Escherichia coli K-12 encodes proteins invol ved in the maintenance of cell-envelope integrity. In addition, tol/pa l mutations result in a mucoid colony phenotype at low temperature. Th e synthesis of capsular polysaccharides by the cpa genes is controlled by the positive regulator RcsA and the two-component RcsC/RcsB system . It was shown that the mucoid phenotype of the tol/pal mutants was du e to an rcsCB-dependent activation of the cpa genes. Furthermore, we h ave identified a mutation in the rcsC gene that decreased the activity of a tolA-lac operon fusion independently of RcsA and partially indep endently of RcsB activators. The corresponding rcsC338 mutation result ed in a Glu to Lys substitution at residue 338 of RcsC. This mutation induced mucoidy even at high temperature, We propose that RcsC modulat es the phosphorylated forms of RcsB and an uncharacterized regulatory protein involved in the control of the tolQRA genes in an opposite man ner. Moreover, our findings strengthen the previous suggestion that Rc sC senses some alterations in the cell surface such as those induced b y tol, pal or rfa mutations, and activates capsule synthesis to protec t the cell against deleterious agents.