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Vol. 15, Issue 1, 58-70, January 2004

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Modification of a Ubiquitin-like Protein Paz2 Conducted Micropexophagy through Formation of a Novel Membrane Structure

Hiroyuki Mukaiyama ^*, Misuzu Baba  , Masako Osumi , Satoshi Aoyagi ^*, Nobuo Kato ^*, Yoshinori Ohsumi , and Yasuyoshi Sakai ^*  

^* Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kitashirakawa-Oiwake, Sakyo-ku, Kyoto 606-8502, Japan; Department of Chemical and Biological Sciences, Faculty of Science, Japan Women's University, Mejirodai, Bunkyo-ku, Tokyo 112-8681, Japan; and Department of Cell Biology, National Institute for Basic Biology, Okazaki, 444-8585, Japan

Submitted May 28, 2003; Revised August 17, 2003; Accepted August 22, 2003
Monitoring Editor: Randy Schekman

Microautophagy is a versatile process in which vacuolar or lysosomal membranes directly sequester cytosolic targets for degradation. Recent genetic evidence suggested that microautophagy uses molecular machineries essential for macroautophagy, but the details of this process are still unknown. In this study, a ubiquitin-like protein Paz2 essential for micropexophagy in the yeast Pichia pastoris has been shown to receive modification through the function of Paz8 and Gsa7, yielding a modified form Paz2-I, similar to the ubiquitin-like lipidation of Aut7 that is essential for macroautophagy in Saccharomyces cerevisiae. We identified a novel membrane structure formed after the onset of micropexophagy, which we suggest is necessary for the sequestration of peroxisomes by the vacuole. Assembly of this newly formed membrane structure, which is followed by localization of Paz2 to it, was found to require a properly functioning Paz2-modification system. We herein show that Paz2 and its modification system conduct micropexophagy through formation of the membrane structure, which explains the convergence between micropexophagy and macroautophagy with regard to de novo membrane formation.

Abbreviations used: FM4-64, N-(3-triethylammoniumpropyl)-4-(p-diethylaminophenylhexatrienyl) pyridinium dibromide; GFP, green fluorescent protein (S65T mutant version); GFP-PTS1, green fluorescent protein fused to PTS1; HA, hemagglutinin-antigen; immuno-EM, immunoelectron microscope; PE, phosphatidylethanolamine; PTS1, peroxisome targeting signal type 1.

Note added in proof. After acceptance of this manuscript, yeast autophagy related genes have been unified as ATG (autophagy-related) genes [D.J. Klionsky, et al. (2003). A unified nomenclature for yeast autophagy-related genes. Dev. Cell, 5, 539–545]. Accordingly, PAZ2, PAZ8, GSA7/PAZ12, and GSA20 have been assigned as PpATG8, PpATG4, PpATG7, and PpATG3, respectively. Table 1 gives unified names for the other related genes.

Corresponding author. E-mail address: ysakai{at}kais.kyotou.ac.jp.

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