Structural identity between the NH2-terminal domain of the rat and human ornithine carbamyltransferase “targeting” sequences.

Analysis of the secondary structure of human and rat ornithine carbamyltransferase's targeting sequence revealed the presence of a highly homologous domain with the following key features: an hydrophobic patch opposite to an hydrophilic surface characterized by the disposition of basic residues at potentially strategic positions. The functional role of this domain was established using a synthetic peptide corresponding to amino acids 1-19 of the rat ornithine carbamyltransferase precursor (pOCT 1-19). When added to an in vitro import assay system, pOCT (1-19) blocked the import of pOCT specifically: it did not impede the entry and processing of the precursor to subunit 2 of the F1-ATPase (p beta). This finding suggests that at least two distinct precursor(s)-specific pathways are required for the import of mitochondrial inner membrane and matrix proteins.