Regulator of the mitochondrial protein import machinery that is localized in the mitochondrial intermembrane space (IMS) and facilitates the transport of proteins from the cytosol into the mitochondrial matrix (PubMed:32826315). Not essential for mitochondrial protein import but induced and required when mitochondrial import is compromised (PubMed:32826315). Stimulates or stabilizes the translocation into the mitochondria of proteins such as OXA1, ATP1 and COX12 (PubMed:32826315). Imported into the mitochondria via the mitochondrial MIA40-ERV1 machinery. Up-regulated by RPN4 transcription factor upon mitochondrial protein-induced stress conditions such as the accumulation in the cytosol of non-imported mitochondrial precursors. The Cx14C/Cx13C motifs are involved in the recognition by the mitochondrial MIA40-ERV1 disulfide relay system and the subsequent transfer of disulfide bonds by dithiol/disulfide exchange reactions to the newly imported protein. Present with 768 molecules/cell in log phase SD medium. Belongs to the MIX23 family.