Fig. 10: Hypothetical model of the mechanism underlying VirB-dependent gene regulation. | Nature Communications

Fig. 10: Hypothetical model of the mechanism underlying VirB-dependent gene regulation.

From: The virulence regulator VirB from Shigella flexneri uses a CTP-dependent switch mechanism to activate gene expression

Fig. 10

a Before VirB associates with the virulence plasmid, the nucleoid-organizing protein H-NS binds and thus stabilizes negative DNA supercoils in the promoter regions of VirB-regulated genes, thereby sequestering the promoters from RNA polymerase and silencing gene expression. b The CTP-dependent loading of VirB clamps at virS sites and their spreading into the adjacent promoter regions leads to local overwinding of the DNA. This effect may destabilize the adjacent H-NS nucleoprotein complexes and reduce the degree of negative supercoiling in the vicinity of the promoter, thereby making it accessible to RNA polymerase and allowing transcription to occur.

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