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The yeast SKN7 gene encodes a transcription factor that is involved in a variety of processes in cell physiology including cell wall synthesis, cell cycle progression, and oxidative stress resistance. Using a transcriptional reporter-based system, it has been demonstrated that Skn7p is regulated by the two-component osmosensor Sln1p in a manner that requires the phosphorelay molecule Ypd1p, but not the response regulator Ssk1p. Consistent with its regulation by an osmosensor, Skn7p is involved in negative regulation of the osmoresponsive HOG MAP kinase cascade. Cells lacking SKN7 and the protein serine/threonine phosphatase encoded by PTC1 are severely disabled for growth, and hyperaccumulate intracellular glycerol. The growth defect of skn7Delta ptc1Delta mutants can be bypassed by overexpression of specific phosphatase genes, or by deletion of the HOG MAP kinase pathway-encoding genes PBS2 or HOG1. / MID2 was isolated in a screen designed to identify upstream regulators of Skn7p. Mid2p is an extensively O-mannosylated protein that is localized to the plasma membrane. Mutants with defective beta-1,6-glucan synthesis grow more quickly when MID2 is absent. Conversely, MID2 is essential for viability in cells lacking FKS1, the gene encoding the primary catalytic subunit of beta-1,3-glucan synthase. mid2Delta mutants are resistant to calcofluor white, a drug that interferes with cell wall chitin synthesis, while cells overexpressing MID2 are supersensitive to the drug. mid2Delta mutants have a significant reduction in stress-induced chitin synthesis, while cells overexpressing MID2 hyperaccumulate cell wall chitin. Consistent with a proposed role in sensing and responding to cell wall stress, high copy expression of specific components of the cell wall integrity MAP kinase cascade suppress various mid2Delta phenotypes, and Mid2p is essential for full activation of the Mpk1p MAP kinase during various cell wall stress and morphogenic conditions. / Observations from genetic and biochemical experiments suggest that Mid2p is a regulator of the small G-protein encoded by RHO1. Deletion of MID2 is lethal to mutants lacking the Rho1p GEF Rom2p, but suppresses the low temperature growth defect of mutants lacking the Rho1p GAP Sac7p. Conversely, high copy expression of MID2 is a strong suppressor of mutants lacking TOR2, an upstream activator of Rom2p, but is toxic to sac7Delta mutants. High copy expression of MID2 causes increased GEF activity towards Rho1p. Mid2p appears to act in parallel to Rom1p and Rom2p in promoting GDP-GTP exchange for Rho1p in a mechanism that is not yet understood.

The effect of mechanical shear on brewing yeast was investigated with a focus on losses incurred through cell rupture and viability loss. The influence of various environmental conditions was studied with regards to the influence on Saccharomyces cerevisiae's ability to resist mechanical shear. Further investigation was performed in order to locate a structure within the yeast cell that contributes to mechanical shear resistance. / It was found that yeast cells grown anaerobically in limited glucose media were more prone to losses in cell viability than cells grown aerobically in the same media, when subjected to mechanical shear. Cells grown anaerobically in high glucose concentrations and allowed to ferment the media to exhaustion were slightly more resistant to mechanical shear compared to cells grown anaerobically without fermentation in minimal glucose media. Higher ethanol concentrations lead to marginally decreased resistance to mechanical shear. / Cell walls of S. cerevisiae were partially digested or extracted using enzymatic treatment or chemical attack. It was found that while the outer mannoprotein layer does not contribute significantly, the inner beta-(1 → 3)-glucan structure plays a significant role in resistance to mechanical shear.

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