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In Escherichia coli, capsular colanic acid polysaccharide synthesis is regulated through the multistep RcsC[right arrow]YojN[right arrow]RcsB phosphorelay. By monitoring a hallmarked cps::lacZ reporter gene, we first searched for physiological stimuli that propagate the Rcs signaling system. The expression of cps::lacZ was activated when cells were grown at a low temperature (20[degrees]C) in the presence of glucose as a carbon source and in the presence of a relatively high concentration of external zinc (1 mm Zn[Cl.sub.2]). In this Rcs signaling system, the rcsF gene product (a putative outer membrane-located lipoprotein) was also an essential signaling component. Based on the defined signaling pathway and physiological stimuli for the Rcs signaling system, we conducted genomewide analyses with microarrays to clarify the Rcs transcriptome (i.e., Rcs regulon). Thirty-two genes were identified as putative Rcs regulon members; these genes included 15 new genes in addition to 17 of the previously described cps genes. Using a set of 37 two-component system mutants, we performed alternative genome-wide analyses. The results showed that the propagation of the zinc-responsive Rcs signaling system was largely dependent on another two-component system, PhoQ/P. Considering the fact that the PhoQ/P signaling system responds to external magnesium, we obtained evidence which supports the view that there is a signaling network that connects the Rcs system with the PhoQ/P system, which coordinately regulates extracellular polysaccharide synthesis in response to the external concentrations of divalent cations.

The yhhP gene of Escherichia coli encodes a 81-residue protein that contributes to the stability of the sigma-s, a stress-induced sigma factor. Analysis of deletion mutants reveals that this protein is essential to the general physiology of Escherichia. Organisms deficient in yhhP fail to thrive in standard laboratory rich media and assume filamentous morphology. This protein has homologs in a wide range of bacterial species.