title: Regulation of cell wall beta-glucan assembly: PTC1 negatively affects PBS2 action in a pathway that includes modulation of EXG1 transcription.
abstract: Analysis of genes involved in yeast cell wall beta-glucan assembly has led to the isolation of EXG1, PBS2 and PTC1. EXG1 and PBS2 were isolated as genes that, when expressed from multicopy plasmids, led to a dominant killer toxin-resistant phenotype. The PTC1 gene was cloned by functional complementation of the calcofluor white-hypersensitive mutant cwh47-1. PTC1/CWH47 is the structural gene for a type 2C serine/threonine phosphatase, EXG1 codes for an exo-beta-glucanase, and PBS2 encodes a MAP kinase kinase in the Pbs2p-Hog1p signal transduction pathway. Overexpression of EXG1 on a 2 mu plasmid led to reduction in a cell wall beta 1,6-glucan and caused killer resistance in wild type cells; while the exg1 delta mutant displayed modest increases in killer sensitivity and beta 1,6-glucan levels. Disruption of PTC1/CWH47 and overexpression of PBS2 gave rise to similar beta-glucan related phenotypes, with higher levels of EXG1 transcription, increased exo-beta-glucanase activity, reduced beta 1,6-glucan levels, and resistance to killer toxin. Genetic analysis revealed that loss of function of the PBS2 gene was epistatic to PTC1/CWH47 disruption, indicating a functional role for the Ptc1p/Cwh47p phosphatase in the Pbs2p-Hog1p signal transduction pathway. These results suggest that Ptc1p/Cwh47p and Pbs2p play opposing regulatory roles in cell wall glucan assembly, and that this is effected in part by modulating Exg1p activity.
authors.affiliation: Department of Biology, McGill University, Montreal, Quebec, Canada.
authors.forename: B
authors.initials: B
authors.lastname: Jiang
authors.forename: A F
authors.initials: AF
authors.lastname: Ram
authors.forename: J
authors.initials: J
authors.lastname: Sheraton
authors.forename: F M
authors.initials: FM
authors.lastname: Klis
authors.forename: H
authors.initials: H
authors.lastname: Bussey
mesh_terms: D002473:Cell Wall / Q000737:chemistry / Q000378:metabolism*; D003001:Cloning, Molecular; D004352:Drug Resistance, Microbial / Q000235:genetics; D004789:Enzyme Activation; D004843:Epistasis, Genetic; D015966:Gene Expression Regulation, Fungal; D005799:Genes, Dominant; D005800:Genes, Fungal; D043326:Glucan 1,3-beta-Glucosidase; D005936:Glucans / Q000096:biosynthesis / Q000378:metabolism*; D055646:Killer Factors, Yeast; D020929:Mitogen-Activated Protein Kinase Kinases; D009154:Mutation; D010641:Phenotype; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D011506:Proteins / Q000494:pharmacology; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D014158:Transcription, Genetic; D001617:beta-Glucosidase / Q000235:genetics / Q000378:metabolism
chemical_list: D005936:Glucans; D055646:Killer Factors, Yeast; D011506:Proteins; D029701:Saccharomyces cerevisiae Proteins; D011494:Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; C089356:PBS2 protein, S cerevisiae; D010744:Phosphoric Monoester Hydrolases; D001617:beta-Glucosidase; D043326:Glucan 1,3-beta-Glucosidase