Cytochrome b is a protein that in humans is encoded by the MT-CYB gene.[5] Its gene product is a subunit of the respiratory chain protein ubiquinol–cytochrome c reductase (UQCR, complex III or cytochrome bc1 complex), which consists of the products of one mitochondrially encoded gene, MT-CYB (mitochondrial cytochrome b), and ten nuclear genes—UQCRC1, UQCRC2, CYC1, UQCRFS1 (Rieske protein), UQCRB, "11kDa protein", UQCRH (cyt c1 Hinge protein), Rieske protein presequence, "cyt c1 associated protein", and Rieske-associated protein.