Chaperone necessary for the incorporation of Rieske iron- sulfur protein UQCRFS1 into the mitochondrial respiratory chain complex III (PubMed:11528392, PubMed:9878253). Plays an important role in the maintenance of mitochondrial tubular networks, respiratory chain assembly and formation of the LETM1 complex (PubMed:18628306). {ECO:0000269|PubMed:11528392, ECO:0000269|PubMed:18628306, ECO:0000269|PubMed:9878253}. This is the function of Ensembl gene identifier ENSG00000074582 (BCS1L, BCS1 ubiquinol-cytochrome c reductase complex chaperone).