D. Varon et al., BACILLUS-SUBTILIS OPERON UNDER THE DUAL CONTROL OF THE GENERAL STRESSTRANSCRIPTION FACTOR SIGMA(B) AND THE SPORULATION TRANSCRIPTION FACTOR SIGMA(H), Molecular microbiology, 20(2), 1996, pp. 339-350
The sigma(B) transcription factor of Bacillus subtilis is activated in
response to a variety of environmental stresses, including those impo
sed by entry into the stationary-growth phase, and by heat, salt or et
hanol challenge to logarithmically growing cells. Although sigma(B) is
thought to control a general stress regulon, the range of cellular fu
nctions it directs remains largely unknown. Our approach to understand
the physiological role of sigma(B) is to characterize genes that requ
ire this factor for all or part of their expression, i.e. the csb gene
s. In this study, we report that the transposon insertion csb40::Tn917
lac identifies an operon with three open reading frames, the second of
which resembles plant proteins induced by desiccation stress. Primer-
extension and operon-fusion experiments showed that the csb40 operon h
as a sigma(B)-dependent promoter which is strongly induced by the addi
tion of salt to logarithmically growing cells. The csb40 operon also h
as a second, sigma(H)-dependent promoter that is unaffected by salt ad
dition. These results provide support for the hypothesis that sigma(B)
controls a general stress regulon, and indicate that the sigma(B) and
sigma(H) regulons partly overlap. We suggest that in addition to its
acknowledged role in the sporulation process, sigma(H) is also involve
d in controlling a subclass of genes that are broadly involved in a ge
neral stress response.