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J. Biol. Chem., Vol. 280, Issue 39, 33669-33678, September 30, 2005

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Trs85 (Gsg1), a Component of the TRAPP Complexes, Is Required for the Organization of the Preautophagosomal Structure during Selective Autophagy via the Cvt Pathway^*

Khuyen Meiling-Wesse, Ulrike D. Epple, Roswitha Krick, Henning Barth, Anika Appelles, Christiane Voss, Eeva-Liisa Eskelinen, and Michael Thumm1

From the Center of Biochemistry and Molecular Cell Biology, Georg-August-University, Heinrich-Dueker-Weg 12, D-37073 Goettingen, Germany and Institute of Biochemistry, University of Kiel, Otto Hahn Platz 9, D-24118 Kiel, Germany

Autophagosomes and Cvt vesicles are limited by two membrane layers. The biogenesis of these unconventional vesicles and the origin of their membranes are hardly understood. Here we identify in Saccharomyces cerevisiae Trs85, a nonessential component of the TRAPP complexes, to be required for the biogenesis of Cvt vesicles. The TRAPP complexes function in endoplasmic reticulum-to-Golgi and Golgi trafficking. Growing trs85 cells show a defect in the organization of the preautophagosomal structure. Although proaminopeptidase I is normally recruited to the preautophagosomal structure, the recruitment of green fluorescent protein-Atg8 depends on Trs85. Autophagy proceeds in the absence of Trs85, albeit at a reduced rate. Our electron microscopic analysis demonstrated that the reduced autophagic rate of trs85 cells does not result from a reduced size of the autophagosomes. Growing and starved cells lacking Trs85 did not show defects in vacuolar biogenesis; mature vacuolar proteinase B and carboxypeptidase Y were present. Also vacuolar acidification was normal in these cells. It is known that mutations impairing the integrity of the ER or Golgi block both autophagy and the Cvt pathway. But the phenotypes of trs85 cells show striking differences to those seen in mutants with defects in the early secretory pathway. This suggests that Trs85 might play a direct role in the Cvt pathway and autophagy.

Received for publication, February 14, 2005 , and in revised form, July 11, 2005.

^* This work was supported by the Deutsche Forschungsgemeinschaft within the SFB 523 "Protein and Membrane Transport between Cellular Compartments." 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 To whom correspondence should be addressed. Fax: 49-551-39-5979; E-mail: mthumm{at}uni-goettingen.de.

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