This gene encodes a subunit of mitochondrial ATP synthase. Mitochondrial ATP synthase catalyzes ATP synthesis, utilizing an electrochemical gradient of protons across the inner membrane during oxidative phosphorylation. ATP synthase is composed of two linked multi-subunit complexes: the soluble catalytic core, F1, and the membrane-spanning component, Fo, comprising the proton channel. This gene encodes the subunit s, also known as factor B, of the proton channel. This subunit is necessary for the energy transduction activity of the ATP synthase complexes. Alternatively spliced transcript variants encoding different isoforms have been identified. [provided by RefSeq, Jul 2008].