Identification of the human mitochondrial protein import receptor, huMas20p. Complementation of Δmas20 in yeast

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Abstract
The human homolog of the S. cerevisiaelN. crassa mitochondrial protein import receptor, Mas20p/MOM19, has been identified and characterized. Sequence similarities between these three proteins is most pronounced within the NH2‐terminal third of the molecules. However, the mammalian protein exhibits only weak homology to the tetratricopeptide repeat B domain that is found in Mas20p/MOM19. huMas20p is targeted and inserted into the outer membrane of isolated rat heart mitochondria, in the Nin‐Ccyto orientation. Antibodies directed against the soluble portion of huMas20p inhibited in vitro mitochondrial import of a diverse set of precursor proteins (including inner membrane uncoupling protein), but failed to block import of a fusion protein bearing the signal‐anchor sequence of Mas20p itself. Finally, expression of huMAS20 complemented the respiratory defect of Δmas20 yeast cells. Together, these results demonstrate that huMAS20p is a component of the mammalian import apparatus.