Saccharomyces cerevisiae Big1p, a putative endoplasmic reticulum membrane protein required for normal levels of cell wall beta-1,6-glucan.
Deletion of Saccharomyces cerevisiae BIG1 causes an approximately 95% reduction in cell wall beta-1,6-glucan, an essential polymer involved in the cell wall attachment of many surface mannoproteins. The big1 deletion mutant grows very slowly, but growth can be enhanced if cells are given osmotic support. We have begun a cell biological and genetic analysis of its product. We demonstrate, using a Big1p-GFP fusion construct, that Big1p is an N-glycosylated integral membrane protein with a Type I topology that is located in the endoplasmic reticulum (ER). Some phenotypes of a big1Delta mutant resemble those of strains disrupted for KRE5, which encodes another ER protein affecting beta-l,6-glucan levels to a similar extent. In a big1Deltakre5Delta double mutant, both the growth and alkali-soluble beta-l,6-glucan levels were reduced as compared to either single mutant. Thus, while Big1p and Kre5p may have similar effects on beta-l,6-glucan synthesis, these effects are at least partially distinct. Residual beta-l,6-glucan levels in the big1Deltakre5Delta double mutant indicate that these gene products are unlikely to be beta-l,6-glucan synthase subunits, but rather may play some ancillary roles in beta-l,6-glucan synthase assembly or function, or in modifying proteins for attachment of beta-l,6-glucan.
Azuma
Masayuki
M
Department of Bioapplied Chemistry, Osaka City University, 3-3-138 Sugimoto Sumiyoshi-ku Osaka, 558-8585, Japan.
Levinson
Joshua N
JN
Pagé
Nicolas
N
Bussey
Howard
H
D000595:Amino Acid Sequence; D002473:Cell Wall / Q000378:metabolism; D003001:Cloning, Molecular; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics; D017353:Gene Deletion; D005800:Genes, Fungal; D005936:Glucans / Q000032:analysis / Q000378:metabolism; D006023:Glycoproteins / Q000235:genetics; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D013347:Subcellular Fractions / Q000378:metabolism; D047071:beta-Glucans
D005656:Fungal Proteins; D005936:Glucans; D006023:Glycoproteins; C064198:KRE5 protein, S cerevisiae; D008562:Membrane Glycoproteins; D029701:Saccharomyces cerevisiae Proteins; D047071:beta-Glucans; C064197:beta-1,6-glucan