title: Yeast beta-glucan synthesis: KRE6 encodes a predicted type II membrane protein required for glucan synthesis in vivo and for glucan synthase activity in vitro.
abstract: The KRE6 gene product is required for synthesis of the major beta-glucans of the yeast cell wall, as mutations in this gene confer reduced levels of both the (1----6)- and (1----3)-beta-D-glucan polymers. Cloning and sequencing of KRE6 reveals a gene encoding a predicted 80-kDa protein with a central transmembrane domain and the topology of a type II membrane protein. Null mutants of KRE6 grow slowly, have larger cells, and show a reduction in alkali-insoluble wall glucans. The mutants show good viability and are not osmotically sensitive, but they are more susceptible to beta-glucanase digestion and mechanical stress than wild-type cells. The specific activity of the GTP-dependent, membrane-associated, in vitro (1----3)-beta-glucan synthase is reduced 50% in kre6 null mutants, and this reduction correlates with the mutation in meiotic tetrads. Transformants of kre6 null mutants with a KRE6 gene expressed from a centomere-based vector show a 4- to 5-fold increase in in vitro (1----3)-beta-glucan synthase activity over transformants with the vector alone. The phenotype and structure of the KRE6 product, Kre6p, suggest that Kre6p may be a beta-glucan synthase, and if so, it implies that beta-glucan synthases are functionally redundant in yeast. Alternatively, Kre6p may be part of a single multiprotein glucan synthase or modulate its activity. Use of KRE6 should permit a genetic analysis of eukaryotic (1----3)-beta-glucan synthesis.
authors.affiliation: Department of Biology, McGill University, Montreal, Quebec, Canada.
authors.forename: T
authors.initials: T
authors.lastname: Roemer
authors.forename: H
authors.initials: H
authors.lastname: Bussey
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000201:enzymology; D002872:Chromosome Deletion; D003001:Cloning, Molecular; D005800:Genes, Fungal; D015698:Genomic Library; D005936:Glucans / Q000096:biosynthesis*; D005964:Glucosyltransferases / Q000235:genetics* / Q000378:metabolism; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D010957:Plasmids; D015183:Restriction Mapping; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics*; D029702:Schizosaccharomyces pombe Proteins
chemical_list: D005936:Glucans; D008565:Membrane Proteins; D029702:Schizosaccharomyces pombe Proteins; D005964:Glucosyltransferases; C020570:1,3-beta-glucan synthase