<p>The qcr operon in <taxon tax_id="1423">Bacillus subtilis</taxon> encodes the menaquinone:cytochrome c reductase complex, which is closely related to but distinct from mitochondrial cytochrome bc1 and chloroplast b6f complexes. QcrA is similar to Rieske-type iron-sulphur proteins; QcrB is similar in size and sequence to b-type cytochromes from b6f complexes; and QcrC has a novel structure that resembles a fusion between subunit IV of b6f complexes and cytochrome c. The amino (subunit IV) region of QcrC appears to have three transmembrane domains. The carboxyl (cytochrome c) region most closely resembles the small cytochromes c-550 (<db_xref db="INTERPRO" dbkey="IPR012218"/>) found in Bacillus species [<cite idref="PUB00015936"/>].</p> Menaquinone:cytochrome c reductase, cytochrome b/c subunit