Analysis of β-1,3-Glucan Assembly in Saccharomyces cerevisiae Using a Synthetic Interaction Network and Altered Sensitivity to Caspofungin

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Abstract
Large-scale screening of genetic and chemical-genetic interactions was used to examine the assembly and regulation of β-1,3-glucan in Saccharomyces cerevisiae. Using the set of deletion mutants in ∼4600 nonessential genes, we scored synthetic interactions with genes encoding subunits of the β-1,3-glucan synthase (FKS1, FKS2), the glucan synthesis regulator (SMI1/KNR4), and a β-1,3-glucanosyltransferase (GAS1). In the resulting network, FKS1, FKS2, GAS1, and SMI1 are connected to 135 genes in 195 interactions, with 26 of these genes also interacting with CHS3 encoding chitin synthase III. A network core of 51 genes is multiply connected with 112 interactions. Thirty-two of these core genes are known to be involved in cell wall assembly and polarized growth, and 8 genes of unknown function are candidates for involvement in these processes. In parallel, we screened the yeast deletion mutant collection for altered sensitivity to the glucan synthase inhibitor, caspofungin. Deletions in 52 genes led to caspofungin hypersensitivity and those in 39 genes to resistance. Integration of the glucan interaction network with the caspofungin data indicates an overlapping set of genes involved in FKS2 regulation, compensatory chitin synthesis, protein mannosylation, and the PKC1-dependent cell integrity pathway.