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 (By similarity).
Subcellular locations: Mitochondrion matrix