PMID:20937888

Citation	Nataf, Y, Bahari, L, Kahel-Raifer, H, Borovok, I, Lamed, R, Bayer, EA, Sonenshein, AL and Shoham, Y (2010) Clostridium thermocellum cellulosomal genes are regulated by extracytoplasmic polysaccharides via alternative sigma factors. Proc. Natl. Acad. Sci. U.S.A. 107:18646-51
Abstract	Clostridium thermocellum produces a highly efficient cellulolytic extracellular complex, termed the cellulosome, for hydrolyzing plant cell wall biomass. The composition of the cellulosome is affected by the presence of extracellular polysaccharides; however, the regulatory mechanism is unknown. Recently, we have identified in C. thermocellum a set of putative σ and anti-σ factors that include extracellular polysaccharide-sensing components [Kahel-Raifer et al. (2010) FEMS Microbiol Lett 308:84-93]. These factor-encoding genes are homologous to the Bacillus subtilis bicistronic operon sigI-rsgI, which encodes for an alternative σ(I) factor and its cognate anti-σ(I) regulator RsgI that is functionally regulated by an extracytoplasmic signal. In this study, the binding of C. thermocellum putative anti-σ(I) factors to their corresponding σ factors was measured, demonstrating binding specificity and dissociation constants in the range of 0.02 to 1 μM. Quantitative real-time RT-PCR measurements revealed three- to 30-fold up-expression of the alternative σ factor genes in the presence of cellulose and xylan, thus connecting their expression to direct detection of their extracellular polysaccharide substrates. Cellulosomal genes that are putatively regulated by two of these σ factors, σ(I1) or σ(I6), were identified based on the sequence similarity of their promoters. The ability of σ(I1) to direct transcription from the sigI1 promoter and from the promoter of celS (encodes the family 48 cellulase) was demonstrated in vitro by runoff transcription assays. Taken together, the results reveal a regulatory mechanism in which alternative σ factors are involved in regulating the cellulosomal genes via an external carbohydrate-sensing mechanism.
Links	PubMed PMC2972930 Online version:10.1073/pnas.1012175107
Keywords	Amino Acid Sequence; Bacterial Proteins/genetics; Bacterial Proteins/metabolism; Base Sequence; Cellulase/genetics; Cellulase/metabolism; Cellulose/metabolism; Clostridium thermocellum/genetics; Clostridium thermocellum/metabolism; DNA, Bacterial/genetics; Gene Expression Regulation, Bacterial; Gene Expression Regulation, Enzymologic; Genes, Bacterial; Kinetics; Models, Biological; Molecular Sequence Data; Multienzyme Complexes/genetics; Multienzyme Complexes/metabolism; Operon; Polysaccharides, Bacterial/metabolism; Promoter Regions, Genetic; Sigma Factor/genetics; Sigma Factor/metabolism; Thermodynamics
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
CLOTH:A3DBH0		GO:0016987: sigma factor activity	ECO:0000314:		F		Fig. 4. In vitro runoff transcription assay with purified C. thermocellum RNA polymerase and linear DNA containing the putative σI1 promoter sequence resulted in transcription from the sigI1 and celS promoters.	complete CACAO 2055
CLOTH:A3DBH0	enables	GO:0016987: sigma factor activity	ECO:0000314: direct assay evidence used in manual assertion		F		Seeded From UniProt	complete

References

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