THE YARROWIA-LIPOLYTICA GENE PAY5 ENCODES A PEROXISOMAL INTEGRAL MEMBRANE-PROTEIN HOMOLOGOUS TO THE MAMMALIAN PEROXISOME ASSEMBLY FACTOR PAF-1

Pay mutants of the yeast Yarrowia lipolytica fail to assemble function al peroxisomes. One mutant strain, pay5-1, lacks normal peroxisomes an d instead contains irregular vesicular structures surrounded by multip le unit membranes. The pay5-1 mutant is not totally deficient in perox isomal matrix protein targeting, as a subset of matrix proteins contin ues to localize to a subcellular fraction enriched for peroxisomes. Th e functionally complementing gene PAYS encodes a protein, Pay5p, of 38 0 amino acids (41,720 Da). Pay5p is a peroxisomal integral membrane pr otein homologous to mammalian PAF-1 proteins, which are essential for peroxisome assembly and whose mutation in humans results in Zellweger syndrome. Pay5p is targeted to mammalian peroxisomes, demonstrating th e evolutionary conservation of the targeting mechanism for peroxisomal membrane proteins. Our results suggest that in pay5 mutants, normal p eroxisome assembly is blocked, which leads to the accumulation of the membranous vesicular structures observed.