Inner mitochondrial membrane complex III (CIII) is the main enzyme complex in the mitochondrial respiratory chain, and Rieske Fe-S protein (UQCRFS1) is the last catalytic subunit added to the complex. The protein encoded by this gene is a nuclear-encoded mitochondrial matrix protein that stabilizes UQCRFS1 and chaperones it to the CIII complex. Defects in this gene are a cause of mitochondrial complex III deficiency, nuclear type 8. Three transcript variants encoding two different isoforms have been found for this gene. [provided by RefSeq, Jun 2014].