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Abstract:
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The cytochrome bc1 complex [ubiquinol:cytochrome c (c2) oxidoreductase] is an oligomeric membrane bound protein present in the respiratory chains of mitochondria, in the electron transport chain of many purple non-sulfur photosynthetic bacteria and aerobic bacteria. It catalyzes electron transfer from ubiquinol to a soluble c-type cytochrome. The redox reaction generates an electrochemical proton gradient which can be coupled to ATP synthesis and other energy requiring processes.
In this work, the structural genes for the Rieske iron-sulfur protein, cytochrome b and cytochrome Cj subunits of the cytochrome bc1 complex of Rhodo spirillum rubrum have been cloned and sequenced. As in other purple sulfur bacteria, the genes for the catalytic subunits of the cytochrome bc1 complex are contained in an operon named pet oxfbc. The amino acid sequences deduced for these three peptides from the nucleotide sequences of the genes have been confirmed, in part, by direct sequencing of portions of the three peptides separated from a sample of the purified, detergent solubilized complex. The deduced amino acid sequences of the pet operon show homology to corresponding proteins from other purple sulfur bacteria.
Northern blots of R. rubrum mRNA have established that the operon is transcribed as a single polycistronic message, the start site of which has been determined by both primer extension and nuclease protection. Photosynthetic growth of R. rubrum was shown to be inhibited by antimycin A, a specific inhibitor of cytochrome bcx complexes, and antimycin A-resistant mutants oi R. rubrum have been isolated. Preliminary results suggest that it may be possible to express the R. rubrum pet operon in a strain of the photosynthetic bacterium Rhodobacter capsulatus from which the native pet operon has been deleted. |