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Mol Microbiol. 1991 Jun;5(6):1309-17.

Cassette mutagenesis implicates a helix-turn-helix motif in promoter recognition by the novel RNA polymerase sigma factor sigma 54.

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1
AFRC Nitrogen Fixation Laboratory, University of Sussex, Brighton, UK.

Abstract

Cassette mutagenesis has been used to study the role of a helix-turn-helix (HTH) motif in the novel RNA polymerase sigma factor sigma 54 of Klebsiella pneumoniae. Of the four residues which are predicted to be solvent-exposed in the second helix, the first (Glu-378) tolerated all substitutions, and some mutations of this residue increased expression from sigma 54-dependent promoters. Certain substitutions in the third exposed residue (Ser-382) produced a promoter-specific phenotype and all substitutions in the fourth residue (Arg-383) inactivated the protein, identifying this residue as being likely to be involved in base-specific interactions with the promoter. In vivo footprinting indicated that the inactive HTH mutants of sigma 54 were defective in interaction with both the -24 and -12 regions of the glnAp2 promoter.

[Indexed for MEDLINE]

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