cDNA Clining and Characterization of 29 kDa Protein, a Putative Component of the Import Machinery of Mitochondrial Precursor Proteins

A cDNA clone for the 29 kDa protein, a putative component of the import machinery of rat liver mitochondrial precursor proteins, was isolated from a rat liver cDNA library. The nucleotide sequence showed that an open reading frame encodes a polypeptide of 284 amino acid residues, with a molecular weight of 33,345. The N-terminal portion of this protein has a 35mer-peptide with the typical features of a mitochondrial presequence. The molecular weight of the mature form was calculated to be 29,579. The peptide, composed of sixteen amino acids, was synthesized chemically based on the amino acid sequence of this protein and was used as an antigen to prepare antibody. This antibody specifically recognized the 29 kDa protein and inhibited the import of mitochondrial precursor proteins. Furthermore, the 29 kDa protein formed a complex with a precursor proteins on its way to the mitochondrial matrix. These results strongly suggest that the 29 kDa protein is a component of the import machinery.