SACCHAROMYCES-CEREVISIAE MITOCHONDRIA LACK A BACTERIAL-TYPE SEC MACHINERY

The bacterial Sec genes encode a generalized protein export machinery. Although the mitochondria present in eukaryotic cells are derived fro m bacterial ancestors, a comprehensive search of the complete genomic sequence for the eukaryotic yeast Saccharomyces cerevisiae did not rev eal any close homologs of the bacterial Sec genes, strongly suggesting that yeast mitochondria lack a generalized bacterial-type export syst em. This finding has implications for the sorting of imported mitochon drial proteins to the intermembrane space compartment and also for the insertion of mitochondrially encoded proteins into the inner membrane .