hydrogenosomal malic enzyme from the anaerobic fungus Neocallimastix frontalis is targeted to mitochondria of the methylotrophic yeast Hansenula polymorpha

Hydrogenosomal proteins always contain an amino-terminal extension which is believed to be a hydrogenosomal targeting signal. In the anaerobic fungus Neocallimastix frontalis these putative targeting signals are 27 amino acids long, are enriched in Ala, Leu, Ser and Arg, and have an Arg at position -2 relative to amino-acid 1 of the mature protein. These features are typically observed in mitochondrial targeting signals. Here we show that the 27 amino-acid leader sequence of the hydrogenosomal malic enzyme of N. frontalis was capable of targeting the enzyme to mitochondria of the methylotrophic ascomycete yeast Hansenula polymorpha. The same protein without this leader sequence remained cytosolic. These data suggest a close relationship between the protein import machineries of mitochondria and hydrogenosomes in fungi and provide further support for the notion that these two organelles share a common evolutionary origin.