THE CANDIDA-BOIDINII PEROXISOMAL MEMBRANE-PROTEIN PMP30 HAS A ROLE INPEROXISOMAL PROLIFERATION AND IS FUNCTIONALLY HOMOLOGOUS TO PMP27 FROM SACCHAROMYCES-CEREVISIAE

The mechanism of peroxisome proliferation is poorly understood. Candid a boidinii is a methylotrophic yeast that undergoes rapid and massive peroxisome proliferation and serves as a good model system for this pr ocess, Pmp30A and Pmp30B (formerly designated Pmp31 and Pmp32, respect ively) are two closely related proteins in a polyploid strain of this yeast that are strongly induced by diverse peroxisome proliferators su ch as methanol, oleate, and D-alanine. The function of these proteins is not understood. To study this issue, we used a recently described h aploid strain (S2) of C. boidinii that can be manipulated genetically, We now report that strain S2 contains a single PMP30 gene very simila r in sequence (greater than 93% identity at the DNA level) to PMP30A a nd PMP30B. When PMP30 was disrupted, cell growth on methanol was great ly inhibited, and cells grown in both methanol and oleate had fewer, l arger, and more spherical peroxisomes than wild-type cells, A similar phenotype was recently described for Saccharomyces cerevisiae cultured on oleate in which PMP27, which encodes a protein of related sequence that is important for peroxisome proliferation, was disrupted, To det ermine whether Pmp27 is a functional homolog of Pmp30, genetic complem entation was performed, PMP30A was expressed in the PMP27 disruptant o f S. cerevisiae, and PMP27 was expressed in the PMP30 disruptant of C. boidinii S2. Complementation, in terms of both cell growth and organe lle size, shape, and number, was successful in both directions, althou gh reversion to a wild-type phenotype was only partial for the PMP30 d isruptant. We conclude that these proteins are functional homologs and that both Pmp30 and Pmp27 have a direct role in proliferation and org anelle size rather than a role in a specific peroxisomal metabolic pat hway of substrate utilization.