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Journal of Bacteriology, August 2006, p. 5712-5721, Vol. 188, No. 16
0021-9193/06/$08.00+0     doi:10.1128/JB.00405-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Activity of Rhodobacter sphaeroides RpoHII, a Second Member of the Heat Shock Sigma Factor Family

Heather A. Green and Timothy J. Donohue*

Department of Bacteriology, University of Wisconsin—Madison, Madison, Wisconsin 53706

Received 22 March 2006/ Accepted 31 May 2006

We have identified a second RpoH homolog, RpoHII, in the {alpha}-proteobacterium Rhodobacter sphaeroides. Primary amino acid sequence comparisons demonstrate that R. sphaeroides RpoHII belongs to a phylogenetically distinct group with RpoH orthologs from {alpha}-proteobacteria that contain two rpoH genes. Like its previously identified paralog, RpoHI, RpoHII is able to complement the temperature-sensitive phenotype of an Escherichia coli {sigma}32 (rpoH) mutant. In addition, we show that recombinant RpoHI and RpoHII each transcribe two E. coli {sigma}32-dependent promoters (rpoD PHS and dnaK P1) when reconstituted with E. coli core RNA polymerase. We observed differences, however, in the ability of each sigma factor to recognize six R. sphaeroides promoters (cycA P1, groESL1, rpoD PHS, dnaK P1, hslO, and ecfE), all of which resemble the E. coli {sigma}32 promoter consensus. While RpoHI reconstituted with R. sphaeroides core RNA polymerase transcribed all six promoters, RpoHII produced detectable transcripts from only four promoters (cycA P1, groESL1, hslO, and ecfE). These results, in combination with previous work demonstrating that an RpoHI mutant mounts a typical heat shock response, suggest that while RpoHI and RpoHII have redundant roles in response to heat, they may also have roles in response to other environmental stresses.

* Corresponding author. Mailing address: Department of Bacteriology, University of Wisconsin—Madison, Madison, WI 53706. Phone: (608) 262-4663. Fax: (608) 262-9865. E-mail: tdonohue{at}bact.wisc.edu.

Journal of Bacteriology, August 2006, p. 5712-5721, Vol. 188, No. 16
0021-9193/06/$08.00+0     doi:10.1128/JB.00405-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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