title: Atg27 is a second transmembrane cycling protein.
abstract: Autophagy is a degradative pathway conserved among all eukaryotic cells, and is responsible for the turnover of damaged organelles and long-lived proteins. The primary morphological feature of autophagy is the sequestration of cargo within a double-membrane cytosolic vesicle called an autophagosome. More than 25 AuTophaGy-related (ATG) genes that are essential for autophagy have been identified from the yeast Saccharomyces cerevisiae. Despite the identification and characterization of Atg proteins, it remains a mystery how the double-membrane vesicle is made, what the membrane source(s) are, and how the lipid is transported to the forming vesicle. Among Atg proteins, Atg9 was the only characterized transmembrane protein required for the formation of double-membrane vesicles. Evidence has been obtained in yeast and mammalian cells for Atg9 cycling between different peripheral compartments and the phagophore assembly site/preautophagosomal structure (PAS), the proposed site of organization for autophagosome formation. This cycling feature makes Atg9 a potential membrane carrier to deliver lipids that are used in the vesicle formation process. Recently, in our lab we characterized a second transmembrane protein, Atg27. The unique localization and cycling features of Atg27 suggest the involvement of the Golgi complex in the autophagy pathway. In this addendum, we discuss the trafficking of Atg27 in yeast and compare it with that of Atg9, and consider the possible meaning of Atg27 Golgi localization.
authors.affiliation: Life Sciences Institute, Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109-2216, USA.
authors.forename: Wei-Lien
authors.initials: WL
authors.lastname: Yen
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Klionsky
mesh_terms: D001343:Autophagy; D000071183:Autophagy-Related Proteins; D002352:Carrier Proteins / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*
chemical_list: C519194:ATG27 protein, S cerevisiae; C434065:ATG9 protein, S cerevisiae; C480170:Atg23 protein, S cerevisiae; D000071183:Autophagy-Related Proteins; D002352:Carrier Proteins; D008565:Membrane Proteins; D029701:Saccharomyces cerevisiae Proteins