DNA supercoiling and transcription in Escherichia coli: The FIS connection.
The nucleoid-associated protein FIS modulates the topology of DNA in a growth-phase dependent manner functioning homeostatically to counteract excessive levels of negative superhelicity. We propose that this is achieved by at least two mechanisms: the physical constraint of low levels of negative superhelicity by FIS binding to DNA and by a reduction in the expression and effectiveness of DNA gyrase. In addition, high levels of expression of the fis gene do themselves require a high negative superhelical density. On DNA substrates containing phased high affinity binding sites, as exemplified by the upstream activating sequence of the tyrT promoter, FIS forms tightly bent DNA structures, or microloops, that are necessary for the optimal expression of the promoter. We suggest that these microloops compensate in part for the FIS-induced lowering of the superhelical density.
MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK. aat@mrc-lmb.cam.ac.uk
A
A
Travers
R
R
Schneider
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G
Muskhelishvili
D002352:Carrier Proteins / Q000235:genetics*; D004278:DNA, Superhelical / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000235:genetics*; D012321:DNA-Directed RNA Polymerases / Q000737:chemistry; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D035021:Factor For Inversion Stimulation Protein; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D034982:Integration Host Factors; D008958:Models, Molecular; D011401:Promoter Regions, Genetic; D014158:Transcription, Genetic
D002352:Carrier Proteins; D004278:DNA, Superhelical; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D035021:Factor For Inversion Stimulation Protein; D034982:Integration Host Factors; C440502:integration host factor, E coli; D012321:DNA-Directed RNA Polymerases