Identification and molecular characterization of a Zellweger disease gene homolog, PAS5, in Saccharomyces cerevisiae.

Abstract

Peroxisome assembly in Saccharomyces cerevisiae requires the products of several genes. A gene encoding a polypeptide with shnilarity to the mammalian peroxisome assembly factor-l (P AF-1) is identified and characterized. Deletion of the PAS5 gene from the Saccharomyces cerevisiae genome results in changes in peroxisomal function. The peroxisomes are defective in the import of catalase A, which is required for H₂O₂ breakdown, and acyl-CoA oxidase, which is required for fatty acid catabolism. Due to the exclusion of these enzymes from peroxisomes, the yeast mutant strain shows greater resistance to the catalase inhibitor 3-amino triazol and grows more poorly in liquid oleic acid medium than the wildtype strain. However, thiolase and peroxisomal malate dehydrogenase, two other peroxisomal proteins, migrate with peroxisomes in Nycodenz gradients of organelles prepared from the pas5 mutant strain. The product encoded by PAS5 shares 28.4% identity and 50.4% similarity along its entire length with the human PAF-1 protein, which is deficient in some patients with the childhood-lethal Zellweger syndrome. Similar to the yeast pas5 mutant strain, a cell line derived from a paf-1 Zellweger patient does not import catalase A and acyl-CoA oxidase into peroxisomes, but thiolase is associated with the peroxisomal membranes. The similarity of the defects in import into peroxisomes of the yeast and mammalian mutant cells is suggestive that the yeast PAS5 and mammalian PAF-l genes have similar functions.