Abstract
We previously reported the cloning of the PAY5 gene of the yeast Yarrowia lipolytica by complementation of the peroxisome assembly mutant pay5-1 (Eitzen, G. A., Titorenko, V. I., Smith, J. J., Veenhuis, M., Szilard, R. K., and Rachubinski, R. A. (1996) J. Biol. Chem. 271, 20300-20306). The peroxisomal integral membrane protein Pay5p is a homologue of mammalian PAF-1 proteins, which are essential for peroxisome assembly and whose mutation in humans results in peroxisome biogenesis disorders. Mutations in the PAY5 gene result in the accumulation of three distinct peroxisomal subpopulations. These subpopulations are characterized by differences in 1) buoyant density, 2) the relative distribution of peroxisomal matrix and membrane proteins, 3) the efficiency of import of several peroxisomal matrix proteins, and 4) the phospholipid levels of peroxisomal membranes. These data, together with the analysis of temporal changes in the relative abundance of individual peroxisomal subpopulations in pay5 mutants, suggest that these subpopulations represent intermediates in a multistep peroxisome assembly pathway normally operating in yeast cells.
Highlights
We show that mutations in the PAY5 gene encoding the peroxisomal integral membrane protein Pay5p of the yeast Yarrowia lipolytica cause the accumulation of three distinct peroxisomal subpopulations
Analysis of the components of the different peroxisomal subpopulations and determination of the kinetics of their accumulation in pay5 mutants suggest that these subpopulations represent intermediates in the peroxisome assembly pathway normally operating in yeast cells
Peroxisomal Subpopulations in pay5 Mutants May Represent Intermediates in the Peroxisome Assembly Pathway—Morphological and biochemical studies of mammalian and yeast cells have shown a structural and functional heterogeneity among peroxisomes [1, 5,6,7,8,9,10]. These observations do not clarify the importance of this heterogeneity for peroxisome biogenesis, identify what proteins are essential for the accumulation of distinct peroxisomal subpopulations, or elucidate how defects in these proteins would affect peroxisome biogenesis
Summary
We show that mutations in the PAY5 gene encoding the peroxisomal integral membrane protein Pay5p of the yeast Yarrowia lipolytica cause the accumulation of three distinct peroxisomal subpopulations. Analysis of the components of the different peroxisomal subpopulations and determination of the kinetics of their accumulation in pay mutants suggest that these subpopulations represent intermediates in the peroxisome assembly pathway normally operating in yeast cells. Significant progress has been made recently toward the elucidation of the diverse biochemical reactions performed by peroxisomes [2] as well as toward the identification and characterization of peroxisomal targeting signals (PTS) and components of the targeting and translocation machineries for peroxisomal proteins [3]. The importance of peroxisomes for normal human development and physiology is demonstrated by the lethality of various peroxisome biogenesis disorders: Zellweger syndrome, neonatal adrenoleukodystrophy, infantile Refsum disease, and rhizomelic chondrodysplasia punctata [4]
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