DjlA negatively regulates the Rcs signal transduction system in Escherichia coli.

The Rcs signal transduction system of Escherichia coli regulating capsular polysaccharide synthesis (cps) genes is activated by overexpression of the djlA gene encoding a cytoplasmic membrane-anchored DnaJ-like protein. However, by monitoring the expression of a cpsB'-lac fusion in pgsA- and mdoH-null mutants in which the Rcs system is activated, we found that the Rcs activity was further increased by deletion of djlA and decreased by low-level extrachromosomal expression of djlA. Furthermore, deletion of djlA in a wild-type strain led to small but significant increase of the basal-level activity of the Rcs system. These results demonstrate that DjlA functions as a negative regulator of the Rcs system unless abnormally overproduced.