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Journal of Bacteriology, October 2005, p. 7062-7071, Vol. 187, No. 20
0021-9193/05/$08.00+0 doi:10.1128/JB.187.20.7062-7071.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
The Mycobacterium tuberculosis Extracytoplasmic-Function Sigma Factor SigL Regulates Polyketide Synthases and Secreted or Membrane Proteins and Is Required for Virulence
Mi-Young Hahn,
Sahadevan Raman,
Mauricio Anaya, and
Robert N. Husson*
Division of Infectious Diseases, Children's Hospital Boston, Harvard Medical School, Boston, Massachusetts 02115
Received 6 May 2005/
Accepted 2 August 2005
Mycobacterium tuberculosis sigL encodes an extracytoplasmic function (ECF) sigma factor and is adjacent to a gene for a membrane protein (Rv0736) that contains a conserved HXXXCXXC sequence. This motif is found in anti-sigma factors that regulate several ECF sigma factors, including those that control oxidative stress responses. In this work, SigL and Rv0736 were found to be cotranscribed, and the intracellular domain of Rv0736 was shown to interact specifically with SigL, suggesting that Rv0736 may encode an anti-sigma factor of SigL. An M. tuberculosis sigL mutant was not more susceptible than the parental strain to several oxidative and nitrosative stresses, and sigL expression was not increased in response to these stresses. In vivo, sigL is expressed from a weak SigL-independent promoter and also from a second SigL-dependent promoter. To identify SigL-regulated genes, sigL was overexpressed and microarray analysis of global transcription was performed. Four small operons, sigL (Rv0735)-Rv0736, mpt53 (Rv2878c)-Rv2877c, pks10 (Rv1660)-pks7 (Rv1661), and Rv1139c-Rv1138c, were among the most highly upregulated genes in the sigL-overexpressing strain. SigL-dependent transcription start sites of these operons were mapped, and the consensus promoter sequences TGAACC in the 35 region and CGTgtc in the 10 region were identified. In vitro, purified SigL specifically initiated transcription from the promoters of sigL, mpt53, and pks10. Additional genes, including four PE_PGRS genes, appear to be regulated indirectly by SigL. In an in vivo murine infection model, the sigL mutant strain showed marked attenuation, indicating that the sigL regulon is important in M. tuberculosis pathogenesis.
* Corresponding author. Mailing address: Division of Infectious Diseases, Children's Hospital, 300 Longwood Ave., Boston, MA 02115. Phone: (617) 919-2883. Fax: (617) 730-0254. E-mail:
robert.husson{at}childrens.harvard.edu.
Present address: Department of Microbiology, Yonsei University College of Medicine, Seoul, Korea.
Journal of Bacteriology, October 2005, p. 7062-7071, Vol. 187, No. 20
0021-9193/05/$08.00+0 doi:10.1128/JB.187.20.7062-7071.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
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