Import of proteins into mitochondria. Yeast cells grown in the presence of carbonyl cyanide m-chlorophenylhydrazone accumulate massive amounts of some mitochondrial precursor polypeptides.

Cytoplasmically synthesized precursors of mitochondrial polypeptides have previously been observed in trace amounts after pulse labeling of yeast spheroplasts or after in vitro translation of yeast mRNA (Maccecchini, M. L., Rudin, Y., Blobel, G., and Schatz, G. (1979) Proc. Natl. Acad. Sci. U. S. A. 76, 343-347). Some of these precursors are shown here to accumulate in large amounts (up to 150 micrograms/g of cell protein) during growth of a cytoplasmic petite (rho-) mutant in the presence of carbonyl cyanide m-chlorophenylhydrazone, an uncoupler of oxidative phosphorylation. Cytochrome c1 precursor accumulated under these conditions is unstable; it is degraded with a half-life of about 10 min. In contrast, the F1-ATPase beta-subunit precursor is degraded considerably more slowly and, following removal of the uncoupler, can be post-translationally imported into mitochondria where it is processed to the mature polypeptide.