Iron-sulfur subunit of the cytochrome bc1 complex, an essential component of the respiratory electron transport chain required for ATP synthesis. The bc1 complex catalyzes the oxidation of menaquinol and the reduction of cytochrome c in the respiratory chain. The bc1 complex operates through a Q-cycle mechanism that couples electron transfer to generation of the proton gradient that drives ATP synthesis. Binds 1 [2Fe-2S] cluster per subunit. The cytochrome bc1 complex is composed of a cytochrome b (QcrB), the Rieske iron-sulfur protein (QcrA) and a diheme cytochrome c (QcrC) subunit. The bc1 complex forms a supercomplex with cytochrome c oxidase (cytochrome aa3). Belongs to the Rieske iron-sulfur protein family.