title: Kre6 protein essential for yeast cell wall beta-1,6-glucan synthesis accumulates at sites of polarized growth.
abstract: Saccharomyces cerevisiae Kre6 is a type II membrane protein with amino acid sequence homology with glycoside hydrolase and is essential for β-1,6-glucan synthesis as revealed by the mutant phenotype, but its biochemical function is still unknown. The localization of Kre6, determined by epitope tagging, is a matter of debate. We raised anti-Kre6 rabbit antiserum and examined the localization of Kre6 and its tagged protein by immunofluorescence microscopy, subcellular fractionation in sucrose density gradients, and immunoelectron microscopy. Integration of the results indicates that the majority of Kre6 is in the endoplasmic reticulum; however, a small but significant portion is also present in the secretory vesicle-like compartments and plasma membrane. Kre6 in the latter compartments is observed as strong signals that accumulate at the sites of polarized growth by immunofluorescence. The truncated Kre6 without the N-terminal 230-amino acid cytoplasmic region did not show this polarized accumulation and had a severe defect in β-1,6-glucan synthesis. This is the first evidence of a β-1,6-glucan-related protein showing the polarized membrane localization that correlates with its biological function.
authors.affiliation: Department of Biotechnology, University of Tokyo, Yayoi, Bunkyo-Ku, Tokyo 113-8657, Japan.
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Kurita
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Noda
authors.forename: Tomoko
authors.initials: T
authors.lastname: Takagi
authors.forename: Masako
authors.initials: M
authors.lastname: Osumi
authors.forename: Koji
authors.initials: K
authors.lastname: Yoda
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000918:Antibody Specificity; D002462:Cell Membrane / Q000378:metabolism; D016764:Cell Polarity / Q000502:physiology; D002473:Cell Wall / Q000378:metabolism*; D002499:Centrifugation, Density Gradient; D004721:Endoplasmic Reticulum / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D008565:Membrane Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D008969:Molecular Sequence Data; D021381:Protein Transport / Q000502:physiology; D011817:Rabbits; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D022142:Secretory Vesicles / Q000378:metabolism; D047071:beta-Glucans / Q000378:metabolism*
chemical_list: C081933:KRE6 protein, S cerevisiae; D008565:Membrane Proteins; D029701:Saccharomyces cerevisiae Proteins; D047071:beta-Glucans; C064197:beta-1,6-glucan