THE HANSENULA-POLYMORPHA PEX14 GENE ENCODES A NOVEL PEROXISOMAL MEMBRANE-PROTEIN ESSENTIAL FOR PEROXISOME BIOGENESIS

We have cloned the Hansenula polymorpha PEX14 gene by functional compl ementation of the chemically induced pex14-1 mutant, which lacked norm al peroxisomes. The sequence of the PEX14 gene predicts a novel protei n product (Pex14p) of 39 kDa which showed no similarity to any known p rotein and lacked either of the two known peroxisomal targeting signal s. Biochemical and electron microscopical analysis indicated that Pex1 4p is a component of the peroxisomal membrane. The synthesis of Pex14p is induced by peroxisome-inducing growth conditions. In cells of both pex14-1 and a PEX14 disruption mutant, peroxisomal membrane remnants were evident; these contained the H.polymorpha peroxisomal membrane pr otein Pex3p together with a small amount of the major peroxisomal matr ix proteins alcohol oxidase, catalase and dihydroxyacetone synthase, t he bulk of which resided in the cytosol. Unexpectedly, overproduction of Pex14p in wild-type H.polymorpha cells resulted in a peroxisome-def icient phenotype typified by the presence of numerous small vesicles w hich lacked matrix proteins; these were localized in the cytosol. Appa rently, the stoichiometry of Pex14p relative to one or more other comp onents of the peroxisome biogenesis machinery appears to be critical f or protein import.