Mutants of the Yarrowia lipolytica PEX23 gene encoding an integral peroxisomal membrane peroxin mislocalize matrix proteins and accumulate vesicles containing peroxisomal matrix and membrane proteins

pex mutants are defective in peroxisome assembly. The mutant strain pex23-1 of the yeast Yarrowia lipolytica lacks morphologically recognizable peroxi somes and mislocalizes all peroxisomal matrix proteins investigated prefere ntially to the cytosol. pex23 strains accumulate vesicular structures conta ining both peroxisomal matrix and membrane proteins. The PEX23 gene was iso lated by functional complementation of the pex23-1 strain and encodes a pro tein, Pex23p, of 418 amino acids (47,588 Da). Pex23p exhibits high sequence similarity to two hypothetical proteins of the yeast Saccharomyces cerevis iae. Pex23p is an integral membrane protein of peroxisomes that is complete ly, or nearly completely, sequestered from the cytosol. Pex23p is detected at low levels in cells grown in medium containing glucose, and its levels a re significantly increased by growth in medium containing oleic acid, the m etabolism of which requires intact peroxisomes.