Involved in protein import into mitochondria. Acts as a Hsp70-specific chaperone that prevents self-aggregation of the matrix Hsp70 chaperones SSC1 (mtHSP70) and SSQ1, thereby maintaining their function in mitochondrial protein import and Fe/S protein biosynthesis. May act together with PAM18 as co-chaperone to facilitate recognition and folding of imported proteins by SSC1 in the mitochondrial matrix. Binds 1 zinc ion per subunit. Interacts with SSC1; binds to the nucleotide-free state as well as to the ADP- or ATP-bound state of SSC1. Soluble matrix protein loosely associated with the inner membrane. By heat shock (at protein level). Present with 1520 molecules/cell in log phase SD medium.