Regulatory role of RsgI in sigI expression in Bacillus subtilis

Abstract

The sigma gene, sigI, of Bacillus subtilis belongs to the group IV heat-shock response genes and has many orthologues in the bacterial phylum Firmicutes. The B. subtilis sigI gene is considered to constitute an operon with rsgI (regulation of sigI, formerly ykrI). As little is known about either the structure and function of the sigI-rsgI operon or the SigI regulons, the role of RsgI in heat-inducible transcription of the sigI-rsgI operon was investigated, using Northern analysis and a heat-stable b-galactosidase reporter assay. Heat-inducible, SigI-dependent transcription of the sigI-rsgI operon was stimulated greatly by disrupting rsgI. Yeast two-hybrid analysis showed direct interaction between the N-terminal portion of the presumed RsgI protein and SigI. Without RsgI function, induction of transcription of the sigI-rsgI operon upon transient heat stress depended on dnaK activity. However, transcription of the operon was induced during growth at prolonged higher temperature even without DnaK function. Without RsgI function, sigI-rsgI operon transcription was induced after the end of growth independent of any temperature shift in a sporulation medium and toward the end of growth in a rich complex medium. Furthermore, glucose addition resulted in a strong suppression of sigI-rsgI transcription. Therefore it is hypothesized that transcription of the sigI-rsgI operon of B. subtilis is negatively regulated by the putative transmembrane protein RsgI, which moderates SigI's sensitivity to heat shock or nutritional stress.

The Cell Wall Regulator σISpecifically Suppresses the Lethal Phenotype ofmblMutants inBacillus subtilis

“…Transcription of the sigI gene is induced by high temperature, and its gene product is a 70 -type sigma factor involved in the heat shock response (3,64). Because upregulation of I expression, either by deletion of the anti-sigma factor RsgI or by overexpression of sigI, was able to suppress the Mg 2ϩ dependence of the mbl mutant, we predicted that upregulation of I by heat stress should also suppress the ⌬mbl phenotype.…”

“…In two of the ten selected suppressor strains, the transposon was found to have inserted independently into the rsgI gene (previously ykrI), encoding the anti-sigma factor for I (3). Three independent insertions were in yflE, encoding a homologue of the lipoteichoic acid synthase LtaS from S. aureus (24; K. Schirner et al, unpublished data).…”

“…I activity is regulated by its cognate anti-sigma factor RsgI, a predicted transmembrane protein encoded by a gene immediately downstream of sigI (3,64). Homologues of I and RsgI can be found in various spore-forming species of the Firmicutes (62), but their precise function remains elusive.…”

Abnormal morphology of Bacillus subtilis ugtP mutant cells lacking glucolipids

“…The sigma gene sigI of B. subtilis belongs to the group IV heat-shock response genes and seems to be negatively regulated by anti-SigI factor RsgI as are ECF sigmas in B. subtilis (Asai et al, 2007). In the cells lacking GL, some ECF sigmas (SigM, SigV, and SigX; data not shown) and SigI were activated (Fig.…”

“…8). Asai et al (2007) and Tseng and Shaw (2008) have examined the SigI regulon; however, the mechanism of SigI activation is still unclear. Our results indicate that SigI responds to the lack of GL, and is activated by an unknown mechanism.…”