In vitro processing of the precursor to human mitochondrial cytochrome c1

The processing of the precursor to human cytochrome c1 has been studied using a transcript of a previously obtained human cytochrome c1 cDNA. The transcript was prepared with SP64 plasmid containing the cDNA as a template, and was translated in a reticulocyte lysate cell-free translation system. The molecular mass of a major translation product was estimated to be 34 kDa. The product was shown to be imported into mitochondria, being converted into a mature-sized polypeptide (31.5 kDa), which was resistant to trypsin treatment. Thus, the former was considered to represent the precursor to the latter. The import required the energized state of the inner membrane. It was also demonstrated that a matrix proteinase cleaved the precursor to a form which was not distinguishable in size from the mature-sized one.