The peroxisomal import signal of amine oxidase from the yeast Hansenula polymorpha is not universal.

Abstract

AbstractAmine oxidase from the yeast Hansenula polymorpha is a peroxisomal protein. The signal for routing of the protein into peroxisomes has not been identified yet. Expression of a mutant amine oxidase in H. Polymorpha has revealed that the C‐terminal sequence, which possesses an internal SRL tripeptide, is not involved in targeting (Faber et al., unpublished). We have explored heterologous expression of the amine oxidase gene (AMO) in Saccharomyces cerevisiae to investigate the conservation of peroxisomal targeting pathways between yeasts. Surprisingly, wide‐type amine oxidase is not recognized as a peroxisomal protein by S. cerevisiae. The enzyme, which was fully active and acumulated to levels similar to those found in H. polymorpha, stayed entirely in the cytosol. However, fusing a SKL or a SRL sequence to the C‐terminus forced the protein at least partially into peroxisomes of the heterologous host. These data suggest that the functional targeting sequence of amine oxidase may differ from the C‐terminal peroxisomal targeting signal S/C/A‐K/R/H‐L (Gould et al., 1989). Contrary to the established tripeptide motif, the amine oxidase targeting signal appears not to be conserved between the different yeast species.