Mutations That Stimulate flhDC Expression in Escherichia coli K-12
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CitationFahrner, Karen A., and Howard C. Berg. 2015. “ Mutations That Stimulate flhDC Expression in Escherichia Coli K-12 .” Edited by R. L. Gourse. J. Bacteriol. 197 (19) (July 13): 3087–3096. doi:10.1128/jb.00455-15.
AbstractMotility is a beneficial attribute that enables cells to access and explore new environments and to escape detrimental ones. The
organelle of motility in Escherichia coli is the flagellum, and its production is initiated by the activating transcription factors
FlhD and FlhC. The expression of these factors by the flhDC operon is highly regulated and influenced by environmental conditions.
The flhDC promoter is recognized by 70 and is dependent on the transcriptional activator cyclic AMP (cAMP)-cAMP receptor
protein complex (cAMP-CRP). A number of K-12 strains exhibit limited motility due to low expression levels of flhDC.
We report here a large number of mutations that stimulate flhDC expression in such strains. They include single nucleotide
changes in the 10 element of the promoter, in the promoter spacer, and in the cAMP-CRP binding region. In addition, we show
that insertion sequence (IS) elements or a kanamycin gene located hundreds of base pairs upstream of the promoter can effectively
enhance transcription, suggesting that the topology of a large upstream region plays a significant role in the regulation of
flhDC expression. None of the mutations eliminated the requirement for cAMP-CRP for activation. However, several mutations
allowed expression in the absence of the nucleoid organizing protein, H-NS, which is normally required for flhDC expression.
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