Ql. Wu et al., A MYCOBACTERIAL EXTRACYTOPLASMIC FUNCTION SIGMA-FACTOR INVOLVED IN SURVIVAL FOLLOWING STRESS, Journal of bacteriology, 179(9), 1997, pp. 2922-2929
The extracytoplasmic function (ECF) sigma factors constitute a diverse
group of alternative sigma factors that have been demonstrated to reg
ulate gene expression in response to environmental conditions in sever
al bacterial species. Genes encoding an ECF sigma factor of Mycobacter
ium tuberculosis, Mycobacterium avium, and Mycobacterium smegmatis, de
signated sigE, were cloned and analyzed. Southern blot analysis demons
trated the presence of a single copy of this gene in these species and
in Mycobacterium bovis BCG, Mycobacterium leprae, and Mycobacterium f
ortuitum. Sequence analysis showed the sigE gene to be highly conserve
d among M. tuberculosis, M. avium, M. smegmatis, and M. leprae. Recomb
inant M. tuberculosis SigE, when combined with core RNA polymerase fro
m M. smegmatis, reconstituted specific RNA polymerase activity on sigE
in vitro, demonstrating that this gene encodes a functional sigma fac
tor, Two in vivo transcription start sites for sigE were also identifi
ed in M. smegmatis and M. bovis BCG. Comparison of wild-type M. smegma
tis with a sigE mutant strain demonstrated decreased survival of the m
utant under conditions of high-temperature heat shock, acidic pH, expo
sure to detergent, and oxidative stress, An inducible protective respo
nse to oxidative stress present in the wild type was absent in the mut
ant, The mycobacterial SigE protein, although nonessential for viabili
ty in vitro,appears to play a role in the ability of these organisms t
o withstand a variety of stresses,