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Journal of Bacteriology, July 1999, p. 4334-4341, Vol. 181, No. 14
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Regulated Expression of a Highly Conserved Regulatory Gene Cluster Is Necessary for Controlling Photosynthesis Gene Expression in Response to Anaerobiosis in Rhodobacter capsulatus

Shouying Du, Jean-Louis K. Kouadio, and Carl E. Bauer^*

Department of Biology, Indiana University, Bloomington, Indiana 47405

Received 3 February 1999/Accepted 7 May 1999

We utilized primer extension analysis to demonstrate that the divergently transcribed regB and senC-regA-hvrA transcripts contain stable 5' ends 43 nucleotides apart within the regB-senC intergenic region. DNA sequence analysis indicates that this region contains two divergent promoters with overlapping ⁷⁰ type 35 and 10 promoter recognition sequences. In vivo analysis of expression patterns of regB::lacZ and senC-regA-hvrA::lacZ reporter gene fusions demonstrates that the regB and senC-regA-hvrA transcripts are both negatively regulated by the phosphorylated form of the global response regulator RegA. DNase I protection assays with a constitutively active variant of RegA indicate that RegA binds between regB and senC overlapping 10 and 35 promoter recognition sequences. Two mutations were also isolated in a regB-deficient background that increased expression of the senC-regA-hvrA operon 10- and 5-fold, respectively. As a consequence of increased RegA expression, these mutants exhibited elevated aerobic and anaerobic photosynthesis (puf) gene expression, even in the absence of the sensor kinase RegB. These results indicate that autoregulation by RegA is a factor contributing to the maintenance of an optimal low level of RegA expression that allows responsiveness to activation by phosphorylation.

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^* Corresponding author. Mailing address: Department of Biology, Indiana University, Jordan Hall, Bloomington, IN 47405-3700. Phone: (812) 855-6595. Fax: (812) 855-6705. E-mail: cbauer{at}bio.indiana.edu.

Present address: Department of Physiology, University of Michigan Medical School, Ann Arbor, MI 48109-0622.

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Journal of Bacteriology, July 1999, p. 4334-4341, Vol. 181, No. 14
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

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