Component of the green S-bacteria bc-complex which consists of the Rieske protein and cytochrome b subunit and which appears to lack a cytochrome c1-equivalent. This complex has a comparatively low redox potential. a plastoquinol + 2 H(+)(in) + 2 oxidized [plastocyanin] = a plastoquinone + 4 H(+)(out) + 2 reduced [plastocyanin] Binds 1 [2Fe-2S] cluster per subunit. The Rieske protein is a high potential 2Fe-2S protein. Belongs to the Rieske iron-sulfur protein family.