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J. Bacteriol., 10 1997, 6138-6144, Vol 179, No. 19
B Zhang and L Kroos
Regulation of gene expression in the mother cell compartment of sporulating
Bacillus subtilis involves sequential activation and inactivation of
several transcription factors. Among them are two sigma factors, sigmaE and
sigmaK, and a DNA-binding protein, SpoIIID. A decrease in the level of
SpoIIID is thought to relieve its repressive effect on transcription by
sigmaK RNA polymerase of certain spore coat genes. Previous studies showed
that sigmaK negatively regulates the level of spoIIID mRNA. Here, it is
shown that sigmaK does not affect the stability of spoIIID mRNA. Rather,
sigmaK appears to negatively regulate the synthesis of spoIIID mRNA by
accelerating the disappearance of sigmaE RNA polymerase, which transcribes
spoIIID. As sigmaK begins to accumulate by 4 h into sporulation, the sigmaE
level drops rapidly in wild-type cells but remains twofold to fivefold
higher in sigK mutant cells during the subsequent 4 h. In a strain
engineered to produce sigmaK 1 h earlier than normal, twofold less sigmaE
than that in wild-type cells accumulates. SigmaK did not detectably alter
the stability of sigmaE in pulse-chase experiments. However, beta-
galactosidase expression from a sigE-lacZ transcriptional fusion showed a
pattern similar to the level of sigmaE protein in sigK mutant cells and
cells prematurely expressing sigmaK. These results suggest that the
appearance of sigmaK initiates a negative feedback loop controlling not
only transcription of spoIIID, but the entire sigmaE regulon, by directly
or indirectly inhibiting the transcription of sigE.
Copyright © 1997, American Society for Microbiology
A feedback loop regulates the switch from one sigma factor to the next in the cascade controlling Bacillus subtilis mother cell gene expression
Department of Biochemistry, Michigan State University, East Lansing 48824, USA.
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