Regulation of RcsA by the ClpYQ (HslUV) protease in Escherichia coli

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Abstract
Escherichia coliClpYQ protease and Lon protease possess a redundant function for degradation of SulA, a cell division inhibitor. An experimental cue implied that the capsule synthesis activator RcsA, a known substrate of Lon, is probably a specific substrate for the ClpYQ protease. This paper shows that overexpression of ClpQ and ClpY suppresses the mucoid phenotype of alonmutant. Since thecpsB(wcaB) gene, involved in capsule synthesis, is activated by RcsA, the reporter constructcpsB–lacZwas used to assay forβ-galactosidase activity and thus follow RcsA stability. The expression ofcpsB–lacZwas increased in double mutants oflonin combination withclpQor/andclpYmutation(s) compared with the wild-type orlonsingle mutants. Overproduction of ClpYQ or ClpQ decreasedcpsB–lacZexpression. Additionally, a PBAD–rcsAfusion construct showed quantitatively that an inducible RcsA activatescpsB–lacZexpression. The effect of RcsA oncpsB–lacZexpression was shown to be influenced by the ClpYQ activities. Moreover, arcsARed–lacZtranslational fusion construct showed higher activity of RcsARed–LacZ in aclpQ clpYstrain than in the wild-type. By contrast, overproduction of cellular ClpYQ resulted in decreasedβ-galactosidase levels of RcsARed–LacZ. Taken together, the data indicate that ClpYQ acts as a secondary protease in degrading the Lon substrate RcsA.