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Journal of Bacteriology, March 2003, p. 1886-1894, Vol. 185, No. 6
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.6.1886-1894.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Leucine-Responsive Regulatory Protein-Mediated Repression of clp (Encoding CS31A) Expression by L-Leucine and L-Alanine in Escherichia coli

Cécile Crost,1,2 Annie Garrivier,1 Josée Harel,2 and Christine Martin1*

Laboratoire de Microbiologie, Institut National de la Recherche Agronomique, 63122 St-Genès-Champanelle, France,1 Département de Pathologie et Microbiologie, Université de Montréal, St-Hyacinthe QC J2S 7C6, Canada2

Received 16 July 2002/ Accepted 16 December 2002

CS31A produced by septicemic and diarrheic Escherichia coli belongs to the Pap-regulatory family of adhesive factors, which are under methylation-dependent transcriptional regulation. Common features of operons encoding members of this family include two conserved GATC sites in the upstream regulatory region, and transcriptional regulators homologue to the PapB and PapI proteins. Methylation protection of GATC sites was previously shown to be dependent on the leucine-responsive regulatory protein (Lrp). Lrp and ClpB, the PapB equivalent, repressed clp basal transcription. A PapI homologue (AfaF) was required together with Lrp to establish the phase variation control, which gave rise to phase-ON cells that expressed CS31A and phase-OFF cells that did not express CS31A. In phase-OFF cells, the GATCdist site was methylated and the GATCprox site was protected from methylation, whereas in phase-ON cells, the inverse situation was found. Unlike Pap fimbriae, CS31A synthesis was dramatically reduced in media containing L-alanine or L-leucine. L-Alanine prevented the OFF-to-ON switch, locking clp expression in the OFF phase, whereas L-leucine repressed transcription without obvious effect on the switch frequency of phase variation. In phase-variable cells, leucine and alanine promoted methylation of GATCdist and methylation protection of GATCprox, increasing the methylation pattern characteristic of repressed cells. Furthermore, alanine prevented the AfaF-dependent methylation protection of GATCdist and thus the appearance of phase-ON cells. In addition, analysis of clp expression in a Lrp-negative background indicated that alanine and leucine also repressed clp transcription by a methylation-independent mechanism.

* Corresponding author. Mailing address: Laboratoire de Microbiologie, Institut National de la Recherche Agronomique, 63122 St-Genès-Champanelle, France. Phone: (33) 4 73 62 42 47. Fax: (33) 4 73 62 45 81. E-mail: cmartin{at}clermont.inra.fr.

Journal of Bacteriology, March 2003, p. 1886-1894, Vol. 185, No. 6
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.6.1886-1894.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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