Synonyms:C5orf31, MZM1L Background:Assembly factor required for Rieske Fe-S protein UQCRFS1 incorporation into the cytochrome b-c1(CIII) complex. Functions as a chaperone, binding to this subunit within the mitochondrial matrix and stabilizing it prior to its translocation and insertion into the late CIII dimeric intermediate within the mitochondrial inner membrane.