title: LC3, a mammalian homologue of yeast Apg8p, is localized in autophagosome membranes after processing.
abstract: Little is known about the protein constituents of autophagosome membranes in mammalian cells. Here we demonstrate that the rat microtubule-associated protein 1 light chain 3 (LC3), a homologue of Apg8p essential for autophagy in yeast, is associated to the autophagosome membranes after processing. Two forms of LC3, called LC3-I and -II, were produced post-translationally in various cells. LC3-I is cytosolic, whereas LC3-II is membrane bound. The autophagic vacuole fraction prepared from starved rat liver was enriched with LC3-II. Immunoelectron microscopy on LC3 revealed specific labelling of autophagosome membranes in addition to the cytoplasmic labelling. LC3-II was present both inside and outside of autophagosomes. Mutational analyses suggest that LC3-I is formed by the removal of the C-terminal 22 amino acids from newly synthesized LC3, followed by the conversion of a fraction of LC3-I into LC3-II. The amount of LC3-II is correlated with the extent of autophagosome formation. LC3-II is the first mammalian protein identified that specifically associates with autophagosome membranes.
authors.affiliation: Department of Cell Biology, National Institute for Basic Biology, Okazaki 444-8585, PRESTO, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Kabeya
authors.forename: N
authors.initials: N
authors.lastname: Mizushima
authors.forename: T
authors.initials: T
authors.lastname: Ueno
authors.forename: A
authors.initials: A
authors.lastname: Yamamoto
authors.forename: T
authors.initials: T
authors.lastname: Kirisako
authors.forename: T
authors.initials: T
authors.lastname: Noda
authors.forename: E
authors.initials: E
authors.lastname: Kominami
authors.forename: Y
authors.initials: Y
authors.lastname: Ohsumi
authors.forename: T
authors.initials: T
authors.lastname: Yoshimori
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D016253:Microscopy, Immunoelectron; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010588:Phagosomes / Q000378:metabolism* / Q000648:ultrastructure; D011499:Protein Processing, Post-Translational; D051381:Rats; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions / Q000378:metabolism; D014162:Transfection
chemical_list: D017931:DNA Primers; D005656:Fungal Proteins; D008869:Microtubule-Associated Proteins