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J. Biol. Chem., Vol. 281, Issue 21, 14805-14812, May 26, 2006

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Pex19p Binds Pex30p and Pex32p at Regions Required for Their Peroxisomal Localization but Separate from Their Peroxisomal Targeting Signals^*

Franco J. Vizeacoumar¹, Wanda N. Vreden, John D. Aitchison, and Richard A. Rachubinski, Canada Research Chair in Cell Biology. International Research Scholar of the Howard Hughes Medical Institute²

From the Department of Cell Biology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada and the Institute for Systems Biology, Seattle, Washington 98103

The assembly of proteins in the peroxisomal membrane is a multistep process requiring their recognition in the cytosol, targeting to and insertion into the peroxisomal membrane, and stabilization within the lipid bilayer. The peroxin Pex19p has been proposed to be either the receptor that recognizes and targets newly synthesized peroxisomal membrane proteins (PMP) to the peroxisome or a chaperone required for stabilization of PMPs at the peroxisomal membrane. Differentiating between these two roles for Pex19p could be achieved by determining whether the peroxisomal targeting signal (PTS) and the region of Pex19p binding of a PMP are the same or different. We addressed the role for Pex19p in the assembly of two PMPs, Pex30p and Pex32p, of the yeast Saccharomyces cerevisiae. Pex30p and Pex32p control peroxisome size and number but are dispensable for peroxisome formation. Systematic truncations from the carboxyl terminus, together with in-frame deletions of specific regions, have identified PTSs essential for targeting Pex30p and Pex32p to peroxisomes. Both Pex30p and Pex32p interact with Pex19p in regions that do not overlap with their PTSs. However, Pex19p is required for localizing Pex30p and Pex32p to peroxisomes, because mutations that disrupt the interaction of Pex19p with Pex30p and Pex32p lead to their mislocalization to a compartment other than peroxisomes. Mutants of Pex30p and Pex32p that localize to peroxisomes but produce cells exhibiting the peroxisomal phenotypes of cells lacking these proteins demonstrate that the regions in these proteins that control peroxisomal targeting and cell biological activity are separable. Together, our data show that the interaction of Pex19p with Pex30p and Pex32p is required for their roles in peroxisome biogenesis and are consistent with a chaperone role for Pex19p in stabilizing or maintaining membrane proteins in peroxisomes.

Received for publication, February 24, 2006 , and in revised form, March 20, 2006.

^* This work was supported by Grant MOP-15131 from the Canadian Institutes of Health Research (to R. A. R.) and Grant GM067228 from the National Institutes of Health (to J. D. A.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Recipient of a Studentship from the Alberta Heritage Foundation for Medical Research.

² To whom correspondence should be addressed: Dept. of Cell Biology, University of Alberta, Medical Sciences Bldg. 5-14, Edmonton, AB T6G 2H7, Canada. Tel.: 780-492-9868; Fax: 780-492-9278; E-mail: rick.rachubinski{at}ualberta.ca.

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