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Dominant Role of the cbb₃ Oxidase in Regulation of Photosynthesis Gene Expression through the PrrBA System in Rhodobacter sphaeroides 2.4.1

Department of Microbiology, Pusan National University, 609-735 Busan, Korea,¹ Korea Science Academy, 614-822 Busan, Korea,² Department of Biology, Yonsei University, 120-749 Seoul, Korea,³ Department of Microbiology and Molecular Genetics, University of Texas Health Science Center, 6431 Fannin, Houston, Texas 77030⁴

Received 26 March 2007/ Accepted 24 May 2007

In this study, the H303A mutant form of the cbb₃ oxidase (H303A oxidase), which has the H303A mutation in its catalytic subunit (CcoN), was purified from Rhodobacter sphaeroides. The H303A oxidase showed the same catalytic activity as did the wild-type form of the oxidase (WT oxidase). The heme contents of the mutant and WT forms of the cbb₃ oxidase were also comparable. However, the puf and puc operons, which are under the control of the PrrBA two-component system, were shown to be derepressed aerobically in the R. sphaeroides strain expressing the H303A oxidase. Since the strain harboring the H303A oxidase exhibited the same cytochrome c oxidase activity as the stain harboring the WT oxidase did, the aerobic derepression of photosynthesis gene expression observed in the H303A mutant appears to be the result of a defective signaling function of the H303A oxidase rather than reflecting any redox changes in the ubiquinone/ubiquinol pool. It was also demonstrated that ubiquinone inhibits not only the autokinase activity of full-length PrrB but also that of the truncated form of PrrB lacking its transmembrane domain, including the proposed quinone binding sequence. These results imply that the suggested ubiquinone binding site within the PrrB transmembrane domain is not necessary for the inhibition of PrrB kinase activity by ubiquinone. Instead, it is probable that signaling through H303 of the CcoN subunit of the cbb₃ oxidase is part of the pathway through which the cbb₃ oxidase affects the relative kinase/phosphatase activity of the membrane-bound PrrB.

Published ahead of print on 8 June 2007.

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