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Journal of Bacteriology, October 2008, p. 6769-6778, Vol. 190, No. 20
0021-9193/08/$08.00+0     doi:10.1128/JB.00828-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Regulation of the Rhodobacter sphaeroides 2.4.1 hemA Gene by PrrA and FnrL{triangledown}

Britton Ranson-Olson1,{dagger} and Jill H. Zeilstra-Ryalls2*

Department of Biological Sciences, Oakland University, Rochester, Michigan 48309,1 Department of Biological Sciences, Bowling Green State University, Bowling Green, Ohio 434032

Received 13 June 2008/ Accepted 30 July 2008

Part of the oxygen responsiveness of Rhodobacter sphaeroides 2.4.1 tetrapyrrole production involves changes in transcription of the hemA gene, which codes for one of two isoenzymes catalyzing 5-aminolevulinic acid synthesis. Regulation of hemA transcription from its two promoters is mediated by the DNA binding proteins FnrL and PrrA. The two PrrA binding sites, binding sites I and II, which are located upstream of the more-5' hemA promoter (P1), are equally important to transcription under aerobic conditions, while binding site II is more important under anaerobic conditions. By using phosphoprotein affinity chromatography and immunoblot analyses, we showed that the phosphorylated PrrA levels in the cell increase with decreasing oxygen tensions. Then, using both in vivo and in vitro methods, we demonstrated that the relative affinities of phosphorylated and unphosphorylated PrrA for the two binding sites differ and that phosphorylated PrrA has greater affinity for site II. We also showed that PrrA regulation is directed toward the P1 promoter. We propose that the PrrA component of anaerobic induction of P1 transcription is attributable to higher affinity of phosphorylated PrrA than of unphosphorylated PrrA for binding site II. Anaerobic activation of the more-3' hemA promoter (P2) is thought to involve FnrL binding to an FNR consensuslike sequence located upstream of the P2 promoter, but the contribution of FnrL to P1 induction may be indirect since the P1 transcription start is within the putative FnrL binding site. We present evidence suggesting that the indirect action of FnrL works through PrrA and discuss possible mechanisms.

* Corresponding author. Mailing address: Department of Biological Sciences, 217 Life Sciences Building, Bowling Green State University, Bowling Green, OH 43403. Phone: (419) 372-2872. Fax: (419) 372-2024. E-mail: jzeilst{at}bgnet.bgsu.edu

{triangledown} Published ahead of print on 8 August 2008.

{dagger} Present address: Department of Biological Sciences, Lake Superior State University, 615 W. Easterday Avenue, Sault Ste. Marie, MI 49783.

Journal of Bacteriology, October 2008, p. 6769-6778, Vol. 190, No. 20
0021-9193/08/$08.00+0     doi:10.1128/JB.00828-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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