This gene encodes a small heme protein that functions as a central component of the electron transport chain in;mitochondria. The encoded protein associates with the inner membrane of the mitochondrion where it accepts electrons;from cytochrome b and transfers them to the cytochrome oxidase complex. This protein is also involved in initiation of;apoptosis. Mutations in this gene are associated with autosomal dominant nonsyndromic thrombocytopenia. Numerous;processed pseudogenes of this gene are found throughout the human genome.