Nucleic Acids Research Advance Access published online on September 23, 2008
Nucleic Acids Research, doi:10.1093/nar/gkn601
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Gene Regulation, Chromatin and Epigenetics |
S-box and T-box riboswitches and antisense RNA control a sulfur metabolic operon of Clostridium acetobutylicum
1Genetics of Bacterial Genomes, Pasteur Institute, CNRS URA2171, 25 rue du Dr Roux, 75724 Paris Cedex 15, France, 2University Paris 7-Denis Diderot, CNRS UPR9073, Institute of Physical and Chemical Biology (IBPC), 13 rue Pierre et Marie Curie, 75005 Paris, France and 3Laboratory of Biotechnology and Bioprocesses, UMR-INSA/CNRS 5504, UMR INSA/INRA 792, 135 Avenue de Rangueil, 31077 Toulouse Cedex 4, France
*To whom correspondence should be addressed. Tel: +33 1 44 38 93 22; Fax: +33 1 45 68 89 48; Email: osoutou{at}pasteur.fr
Received July 10, 2008. Revised September 4, 2008. Accepted September 4, 2008.
The ubiGmccBA operon of Clostridium acetobutylicum is involved in methionine to cysteine conversion. We showed that its expression is controlled by a complex regulatory system combining several RNA-based mechanisms. Two functional convergent promoters associated with transcriptional antitermination systems, a cysteine-specific T-box and an S-box riboswitch, are located upstream of and downstream from the ubiG operon, respectively. Several antisense RNAs were synthesized from the downstream S-box-dependent promoter, resulting in modulation of the level of ubiG transcript and of MccB activity. In contrast, the upstream T-box system did not appear to play a major role in regulation, leaving antisense transcription as the major regulatory mechanism for the ubiG operon. The abundance of sense and antisense transcripts was inversely correlated with the sulfur source availability. Deletion of the downstream promoter region completely abolished the sulfur-dependent control of the ubiG operon, and the expression of antisense transcripts in trans did not restore the regulation of the operon. Our data revealed important insights into the molecular mechanism of cis-antisense-mediated regulation, a control system only rarely observed in prokaryotes. We proposed a regulatory model in which the antisense RNA controlled the expression of the ubiG operon in cis via transcriptional interference at the ubiG locus.
Present address: Sergine Even, UMR INRA 1253, Laboratory of Microbiology, 65, rue de Saint Brieuc, CS 84215, 35042 Rennes cedex, France
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