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J. Bacteriol., 05 1997, 2922-2929, Vol 179, No. 9
QL Wu, D Kong, K Lam and RN Husson
The extracytoplasmic function (ECF) sigma factors constitute a diverse
group of alternative sigma factors that have been demonstrated to regulate
gene expression in response to environmental conditions in several
bacterial species. Genes encoding an ECF sigma factor of Mycobacterium
tuberculosis, Mycobacterium avium, and Mycobacterium smegmatis, designated
sigE, were cloned and analyzed. Southern blot analysis demonstrated the
presence of a single copy of this gene in these species and in
Mycobacterium bovis BCG, Mycobacterium leprae, and Mycobacterium fortuitum.
Sequence analysis showed the sigE gene to be highly conserved among M.
tuberculosis, M. avium, M. smegmatis, and M. leprae. Recombinant M.
tuberculosis SigE, when combined with core RNA polymerase from M.
smegmatis, reconstituted specific RNA polymerase activity on sigE in vitro,
demonstrating that this gene encodes a functional sigma factor. Two in vivo
transcription start sites for sigE were also identified in M. smegmatis and
M. bovis BCG. Comparison of wild-type M. smegmatis with a sigE mutant
strain demonstrated decreased survival of the mutant under conditions of
high-temperature heat shock, acidic pH, exposure to detergent, and
oxidative stress. An inducible protective response to oxidative stress
present in the wild type was absent in the mutant. The mycobacterial SigE
protein, although nonessential for viability in vitro, appears to play a
role in the ability of these organisms to withstand a variety of stresses.
Copyright © 1997, American Society for Microbiology
A mycobacterial extracytoplasmic function sigma factor involved in survival following stress
Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
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