Component of the ubiquinol-cytochrome c reductase complex (complex III or cytochrome b-c1 complex), which is a respiratory chain that generates an electrochemical potential coupled to ATP synthesis. a quinol + 2 Fe(III)-[cytochrome c](out) = a quinone + 2 Fe(II)-[cytochrome c](out) + 2 H(+)(out) Binds 1 [2Fe-2S] cluster per subunit. The main subunits of complex b-c1 are: cytochrome b, cytochrome c1 and the Rieske protein. Required for nitrogen fixation in root nodules on soybeans, but not for aerobic growth. It seems however to be expressed under many growth conditions (aerobic, microaerobic and in nodule bacteroids). The Rieske protein is a high potential 2Fe-2S protein. Belongs to the Rieske iron-sulfur protein family.