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Journal of Bacteriology, May 1999, p. 3039-3050, Vol. 181, No. 10
Division of Molecular Microbiology,
Biozentrum, University of Basel, CH-4056 Basel, Switzerland
Received 19 January 1999/Accepted 2 March 1999
The region of the Caulobacter crescentus chromosome
harboring the genes for the ClpXP protease was isolated and
characterized. Comparison of the deduced amino acid sequences of the
C. crescentus ClpP and ClpX proteins with those of their
homologues from several gram-positive and gram-negative bacteria
revealed stronger conservation for the ATPase regulatory subunit (ClpX)
than for the peptidase subunit (ClpP). The C. crescentus
clpX gene was shown 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 the
C. crescentus chromosome by an open reading frame pointing in the opposite direction from the clp genes, and
transcription of clpP and clpX was found to be
uncoupled. clpP is transcribed as a monocistronic unit with
a promoter (PP1) located immediately upstream of the 5' end
of the gene and a terminator structure following its 3' end.
PP1 is under heat shock control and is induced upon entry
of the cells into the stationary phase. At least three promoters for
clpX (PX1, PX2, and
PX3) were mapped in the clpP-clpX intergenic
region. In contrast to PP1, the clpX promoters
were found to be downregulated after heat shock but were also subject to growth phase control. In addition, the clpP and
clpX promoters showed different activity patterns during
the cell cycle. Together, these results demonstrate that the genes
coding for the peptidase and the regulatory subunits of the ClpXP
protease are under independent transcriptional control in C. crescentus. Determination of the numbers of ClpP and ClpX
molecules per cell suggested that ClpX is the limiting component
compared with ClpP.
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Identification and Transcriptional Control of the
Genes Encoding the Caulobacter crescentus ClpXP
Protease
*
Corresponding author. Mailing address: Division of
Molecular Microbiology, Biozentrum, University of Basel, CH-4056 Basel, Switzerland. Phone: 41-61-267-21-35. Fax: 41-61-267-21-18. E-mail: jenal{at}ubaclu.unibas.ch.
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