Msn2p and the partially redundant factor Msn4p are key regulators of stress-responsive gene expression in Saccharomyces cerevisiae. They are required for the transcription of a number of genes coding for proteins with stress-protective functions. Both Msn2p and Msn4p are Cys₂His₂ zinc finger proteins and bind to the stress response element (STRE). In vivo footprinting studies show that the occupation of STREs is enhanced in stressed cells and dependent on the presence of Msn2p and Msn4p. Both factors accumulate in the nucleus under stress conditions, such as heat shock, osmotic stress, carbon-source starvation, and in the presence of ethanol or sorbate. Stress-induced nuclear localization was found to be rapid, reversible, and independent of protein synthesis. Nuclear localization of Msn2p and Msn4p was shown to be correlated inversely to cAMP levels and protein kinase A (PKA) activity. A region with significant homologies shared between Msn2p and Msn4p is sufficient to confer stress-regulated localization to a SV40–NLS–GFP fusion protein. Serine to alanine or aspartate substitutions in a conserved PKA consensus site abolished cAMP-driven nuclear export and cytoplasmic localization in unstressed cells. We propose stress and cAMP-regulated intracellular localization of Msn2p to be a key step in STRE-dependent transcription and in the general stress response.

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The echinocandin caspofungin is a new antifungal drug that blocks cell wall synthesis through inhibition of β-(1-3)-glucan synthesis. Saccharomyces cerevisiae cells are able to tolerate rather high caspofungin concentrations, displaying high viability at low caspofungin doses. To identify yeast genes implicated in caspofungin tolerance, we performed a genome-wide microarray analysis. Strikingly, caspofungin treatment rapidly induces a set of genes from the protein kinase C (PKC) cell integrity signaling pathway, as well as those required for cell wall maintenance and architecture. The mitogen-activated protein kinase Slt2p is rapidly activated by phosphorylation, triggering signaling through the PKC pathway. Cells lacking genes such as SLT2 , BCK1 , and PKC1 , as well as the caspofungin target gene, FKS1 , display pronounced hypersensitivity, demonstrating that the PKC pathway is required for caspofungin tolerance. Notably, the cell surface integrity sensor Wsc1p, but not the sensors Wsc2-4p and Mid2p, is required for sensing caspofungin perturbations. The expression modulation of PKC target genes requires the transcription factor Rlm1p, which controls expression of several cell wall synthesis and maintenance genes. Thus, caspofungin-induced cell wall damage requires Wsc1p as a dedicated sensor to launch a protective response through the activated salvage pathway for de novo cell wall synthesis. Our results establish caspofungin as a specific activator of Slt2p stress signaling in baker's yeast.

Stress response elements (STREs, core consensus AG₄ or C₄T) have been demonstrated previously to occur in the upstream region of a number of genes responsive to induction by a variety of stress signals. This stress response is mediated by the homologous transcription factors Msn2p and Msn4p, which bind specifically to STREs. Double mutants (msn2 msn4) deficient in these transcription factors have been shown to be hypersensitive to severe stress conditions. To obtain a more representative overview of the set of yeast genes controlled via this regulon, a computer search of the Saccharomyces cerevisiae genome was carried out for genes, which, similar to most known STRE‐controlled genes, exhibit at least two STREs in their upstream region. In addition to the great majority of genes previously known to be controlled via STREs, 69 open reading‐frames were detected. Expression patterns of a set of these were examined by grid filter hybridization, and 14 genes were examined by Northern analysis. Comparison of the expression patterns of these genes demonstrates that they are all STRE‐controlled although their detailed expression patterns differ considerably. © 1998 John Wiley & Sons, Ltd.

The opportunistic human fungal pathogen Candida glabrata is closely related to Saccharomyces cerevisiae, yet it has evolved to survive within mammali