title: Protein sorting to the vacuolar membrane.
abstract: The vacuolar membrane (tonoplast) of plant cells contains a polytopic integral membrane protein with six membrane-spanning domains and cytoplasmically oriented amino-terminal and carboxy-terminal domains. This protein, tonoplast intrinsic protein (TIP), is a member of the membrane intrinsic protein (MIP) family of proteins, a family of channel proteins found in a variety of organisms. In bean seeds, alpha-TIP is synthesized on the rough endoplasmic reticulum and its transport to the tonoplast is mediated by the secretory system. In this study, we report that a polypeptide segment that includes the sixth membrane domain and the cytoplasmic tail of 18 amino acids of alpha-TIP is sufficient to target the reporter protein phosphinotricine acetyltransferase to the tonoplast of stably transformed tobacco cells. To determine if the carboxy-terminal cytoplasmic tail of alpha-TIP contains important tonoplast targeting information, a deletion construct lacking the 15 carboxy-terminal amino acids was introduced for transient expression in tobacco cells; we found that the slightly truncated protein still accumulated in the tonoplast. From these results, we concluded that a transmembrane domain of a tonoplast protein probably contains sufficient information for transport to the tonoplast. Whether such transport occurs by bulk flow or involves specific cellular machinery remains to be determined.
authors.affiliation: Department of Biology, University of California, San Diego, La Jolla, California 92093-0116.
authors.forename: H
authors.initials: H
authors.lastname: Höfte
authors.forename: M J
authors.initials: MJ
authors.lastname: Chrispeels
mesh_terms: D000123:Acetyltransferases / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D001692:Biological Transport; D007425:Intracellular Membranes / Q000378:metabolism*; D007700:Kinetics; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012995:Solubility; D014617:Vacuoles / Q000378:metabolism*
chemical_list: D008565:Membrane Proteins; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; C077491:tonoplast intrinsic protein, plant; D000123:Acetyltransferases; C056243:phosphinothricin N-acetyltransferase