The import receptor MOM72 constitutes part of the protein translocation machinery of the outer mitochondrial membrane, the receptor-general insertion pore complex. The protein contains a membrane anchor at the NH2 terminus and a large cytosolic domain. In yeast and Neurospora crassa the cytosolic domain comprises about 570-580 amino acid residues. The cytosolic domain of yeast MOM72 was purified after expression in Escherichia coli as a homogeneous monomeric protein. It can recognize precursor proteins as demonstrated by its ability to compete for binding and import into the mitochondria and to physically interact with preproteins. A subset of preproteins including the ADP/ATP carrier and the phosphate carrier interact with very high affinity, precursors that are known to be targeted via MOM72. Thus, the cytosolic domain of MOM72 plays a critical function in the recognition of preproteins by directly binding to precursor proteins and thereby facilitating their targeting to mitochondria.