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J. Bacteriol. doi:10.1128/JB.01197-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Substitution of a highly conserved histidine in the E. coli heat shock transcription factor, ³², affects promoter utilization in vitro and leads to over-expression of the biofilm-associated Flu protein in vivo

Center for RNA Molecular Biology and Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106

^* To whom correspondence should be addressed. Email: pld2{at}case.edu.

	Abstract

The heat shock sigma factor (³² in E. coli) directs the bacterial RNA polymerase to promoters of a specific sequence, to form a stable complex, competent to initiate transcription of genes whose products mitigate the effects of exposure of the cell to higher temperatures. The histidine at position 107 of ³² is at the homologous position of a tryptophan residue at position 433 of the main sigma factor of E.coli, ⁷⁰. This tryptophan is essential for the strand separation step leading to the formation of the initiation-competent RNA polymerase-promoter complex. The heat shock sigma factors of all proteobacteria sequenced have a histidine at this position, while in the and proteobacteria it is a tryptophan. In vitro the alanine for histidine substitution at position 107 (H107A) destabilizes complexes between the GroE promoter and RNA polymerase containing ³², implying that H107 plays a role in formation or maintenance of the strand separated complex. In vivo, the H107A substitution in ³² impedes recovery from heat shock (exposure to 42°C) and it also leads to over-expression of the Flu protein, associated with biofilm formation, at lower temperatures (30°C).