Identification and transcriptional control of the genes encoding the Caulobacter crescentus ClpXP protease

The region of the Caulobacter crescentus chromosome harboring the genes for the ClpXP protease was isolated and characterized. Comparison of the deduc ed amino acid sequences of the C. crescentus ClpP and ClpX proteins with th ose of their homologues from several gram-positive and gram-negative bacter ia revealed stronger conservation for the ATPase regulatory subunit (ClpX) than for the peptidase subunit (ClpP). The C. crescentus clpX gene was show n by complementation analysis to be functional in Escherichia coli. However , clpX from E. coli was not able to substitute for the essential nature of the clpX gene in C. crescentus. The clpP and clpX genes are separated on th e C. crescentus chromosome by an open reading frame pointing in the opposit e direction from the clp genes, and transcription of clpP and clpX was foun d to be uncoupled. clpP is transcribed as a monocistronic unit with a promo ter (P-P1) located immediately upstream of the 5' end of the gene and a ter minator structure following its 3' end. P-P1 is under heat shock control an d is induced upon entry of the cells into the stationary phase. At least th ree promoters for clpX (P-X1, P-X2, and P-X3) were mapped in the clpP-clpX intergenic region. In contrast to P-P1, the clpX promoters were found to be downregulated after heat shock but were also subject to growth phase contr ol. In addition, the clpP and clpX promoters showed different activity patt erns during the cell cycle. Together, these results demonstrate that the ge nes coding for the peptidase and the regulatory subunits of the ClpXP prote ase are under independent transcriptional control in C. crescentus. Determi nation of the numbers of ClpP and ClpX molecules er cell suggested that Clp X is the limiting component compared with ClpP.