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Journal of Bacteriology, March 1999, p. 1892-1899, Vol. 181, No. 6
Department of Biology, Georgia State
University, Atlanta, Georgia 30303
Received 5 October 1998/Accepted 12 January 1999
SecB, a protein export-specific chaperone, enhances the export of a
subset of proteins across cytoplasmic membranes of Escherichia coli. Previous studies showed that the synthesis of SecB is
repressed by the presence of glucose in the medium. The derepression of SecB requires the products of both the cya and
crp genes, indicating that secB expression is
under the control of catabolic repression. In this study, two
secB-specific promoters were identified. In addition, 5'
transcription initiation sites from these two promoters were determined
by means of secB-lacZ fusions and primer extension. The
distal P1 promoter appeared to be independent of carbon sources, whereas the proximal P2 promoter was shown to be subject to control by
the cyclic AMP (cAMP) receptor protein (CRP)-cAMP complexes. Gel-mobility shift studies showed that this regulation results from
direct interaction between the secB P2 promoter region and the CRP-cAMP complex. Moreover, the CRP binding site on the
secB gene was determined by DNase I footprinting and
further substantiated by mutational analysis. The identified
secB CRP binding region is centered at the
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Catabolic Repression of secB Expression Is Positively
Controlled by Cyclic AMP (cAMP) Receptor Protein-cAMP Complexes
at the Transcriptional Level
61.5 region of
the secB gene and differed from the putative binding sites
predicted by computer analysis.
*
Corresponding author. Mailing address: Department of
Biology, Georgia State University, P.O. Box 4010, Atlanta, GA
30302-4010. Phone: (404) 651-3109. Fax: (404) 651-2509. E-mail:
biopct{at}panther.gsu.edu.
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