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J. Bacteriol., May 1997, 2915-2921, Vol 179, No. 9
X Huang, A Decatur, A Sorokin and JD Helmann
The sigX gene, identified as part of the international effort to sequence
the Bacillus subtilis genome, has been proposed to encode an alternative
sigma factor of the extracytoplasmic function (ECF) subfamily. The sigX
gene is cotranscribed with a downstream gene, ypuN, during logarithmic and
early stationary phases of growth. We now report that strains lacking
sigma(X) are impaired in the ability to survive at high temperature whereas
a ypuN mutant has increased thermotolerance. We overproduced and purified
sigma(X) from Escherichia coli and demonstrate that in vitro, both sigma(A)
and sigma(X) holoenzymes recognize promoter elements within the sigX-ypuN
control region. However, they have distinct salt optima such that
sigma(A)-dependent transcription predominates at low salt while
sigma(X)-dependent transcription predominates at high salt. A 54-bp region
upstream of sigX suffices as a sigma(X)-dependent promoter in vivo,
demonstrating that sigX is at least partially under positive autoregulatory
control. Mutation of ypuN increases expression from the sigma(X)-dependent
promoter in vivo, suggesting that ypuN may encode a negative regulator of
sigma(X) activity.
Copyright © 1997, American Society for Microbiology
The Bacillus subtilis sigma(X) protein is an extracytoplasmic function sigma factor contributing to survival at high temperature
Field of Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, New York 14853-8101, USA.
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