MOM19, an import receptor for mitochondrial precursor proteins

We have identified a 19 kd protein of the mitochondrial outer
membrane (MOM19). Monospecific IgG and Fab fragments directed
against MOM19 inhibit import of precursor proteins destined for the
various mitochondrial subcompartments, including porin, cytochrome
c1, Fe/S protein, F0 ATPase subunit 9, and F1 ATPase subunit β.
Inhibition occurs at the level of high affinity binding of
precursors to mitochondria. Consistent with previous functional
studies that suggested the existence of distinct import sites for
ADP/ATP carrier and cytochrome c, we find that import of those
precursors is not inhibited. We conclude that MOM19 is identical
to, or closely associated with, a specific mitochondrial import
receptor.