Essential for mitochondrial respiratory chain complex III (CIII) assembly and stability (PubMed:32161263). Also required for cytochrome c oxidase complex (complex IV) assembly (By similarity). Interacts with UQCRC1 (PubMed:32161263). Interacts with UQCRQ (PubMed:32161263). Interacts with SMIM4 (By similarity). Highly expressed in brown adipose, cardiac and skeletal muscle (at protein level).