The role of dor gene products in controlling the P2 promoter of the cytochrome c 2 gene, cycA, in Rhodobacter sphaeroides

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Abstract
This study explores the regulatory networks controlling anaerobic energy production by the facultative phototrophRhodobacter sphaeroides. The specific aim was to determine why activity of the P2 promoter for the gene (cycA) encoding the essential photosynthetic electron carrier, cytochromec2, is decreased when the alternative electron acceptor DMSO is added to photosynthetically grown cells. The presence of DMSO is believed to activate the DorR response regulator, which controls expression of proteins required to reduce DMSO. A DorR−strain showed no change incycAP2 promoter activity when DMSO was added to photosynthetic cells, indicating that DorR was required for the decreased expression in wild-type cells. To test if DorR acted directly at this promoter to change gene expression, recombinant DorR was purified and studiedin vitro. Preparations of DorR that were active at other target promoters showed no detectable interaction withcycAP2, suggesting that this protein is not a direct regulator of this promoter. We also found thatcycAP2 activity in a DorA−strain was not decreased by the addition of DMSO to photosynthetic cells. A model is presented to explain why the presence of a functional DMSO reductase (DorA) is required for DMSO to decreasecycAP2 expression under photosynthetic conditions.