WE have previously identified an integral membrane protein (p32) from Saccharomyces cerevisiae as a receptor for protein import into mitochondria, and have localized it to the mitochondrial outer membrane at contact sites1. Here we report isolation of the corresponding mitochondrial import receptor gene, termed MIR1 The deduced amino-acid sequence of p32 shows roughly 40% identity with proteins of bovine heart2 and rat liver3 that have been suggested to be mitochondrial phosphate carriers. Haploid cells carrying a disrupted MIR1 allele were unable to grow on a non-fermentable carbon source but grew in media containing glucose, indicating that the MIR1 protein is essential for mitochondrial function. Compared with wild type, amounts of some mitochondrial proteins were markedly reduced in cells containing a disrupted MIR1 allele, whereas levels of others were unchanged. This indicates that yeast contains more than one pathway for protein import into mitochondria.
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