We describe the cloning of the Hansenula polymorpha PER1 gene and the characterization of the gene and its product, PER1p. The gene was cloned by functional complementation of a per1 mutant of H. polymorpha, which was impaired in the import of peroxisomal matrix proteins (Pim- phenotype). The DNA sequence of PER1 predicts that PER1p is a polypeptide of 650 amino acids with no significant sequence similarity to other known proteins. PER1 expression was low but significant in wild-type H. polymorpha growing on glucose and increased during growth on any one of a number of substrates which induce peroxisome proliferation. PER1p contains both a carboxy- (PTS1) and an amino-terminal (PTS2) peroxisomal targeting signal which both were demonstrated to be capable of directing bacterial beta-lactamase to the organelle. In wild-type H. polymorpha PER1p is a protein of low abundance which was demonstrated to be localized in the peroxisomal matrix. Our results suggest that the import of PER1p into peroxisomes is a prerequisite for the import of additional matrix proteins and we suggest a regulatory function of PER1p on peroxisomal protein support.

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