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

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* 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.

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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.

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