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      Osmotic Stress Signaling and Osmoadaptation in Yeasts

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      Microbiology and Molecular Biology Reviews
      American Society for Microbiology

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          Abstract

          SUMMARY

          The ability to adapt to altered availability of free water is a fundamental property of living cells. The principles underlying osmoadaptation are well conserved. The yeast Saccharomyces cerevisiae is an excellent model system with which to study the molecular biology and physiology of osmoadaptation. Upon a shift to high osmolarity, yeast cells rapidly stimulate a mitogen-activated protein (MAP) kinase cascade, the high-osmolarity glycerol (HOG) pathway, which orchestrates part of the transcriptional response. The dynamic operation of the HOG pathway has been well studied, and similar osmosensing pathways exist in other eukaryotes. Protein kinase A, which seems to mediate a response to diverse stress conditions, is also involved in the transcriptional response program. Expression changes after a shift to high osmolarity aim at adjusting metabolism and the production of cellular protectants. Accumulation of the osmolyte glycerol, which is also controlled by altering transmembrane glycerol transport, is of central importance. Upon a shift from high to low osmolarity, yeast cells stimulate a different MAP kinase cascade, the cell integrity pathway. The transcriptional program upon hypo-osmotic shock seems to aim at adjusting cell surface properties. Rapid export of glycerol is an important event in adaptation to low osmolarity. Osmoadaptation, adjustment of cell surface properties, and the control of cell morphogenesis, growth, and proliferation are highly coordinated processes. The Skn7p response regulator may be involved in coordinating these events. An integrated understanding of osmoadaptation requires not only knowledge of the function of many uncharacterized genes but also further insight into the time line of events, their interdependence, their dynamics, and their spatial organization as well as the importance of subtle effects.

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          TRK1 and TRK2 encode structurally related K+ transporters in Saccharomyces cerevisiae.

          We describe the cloning and molecular analysis of TRK2, the gene likely to encode the low-affinity K+ transporter in Saccharomyces cerevisiae. TRK2 encodes a protein of 889 amino acids containing 12 putative membrane-spanning domains (M1 through M12), with a large hydrophilic region between M3 and M4. These structural features closely resemble those contained in TRK1, the high-affinity K+ transporter. TRK2 shares 55% amino acid sequence identity with TRK1. The putative membrane-spanning domains of TRK1 and TRK2 share the highest sequence conservation, while the large hydrophilic regions between M3 and M4 exhibit the greatest divergence. The different affinities of TRK1 trk2 delta cells and trk1 delta TRK2 cells for K+ underscore the functional independence of the high- and low-affinity transporters. TRK2 is nonessential in TRK1 or trk1 delta haploid cells. The viability of cells containing null mutations in both TRK1 and TRK2 reveals the existence of an additional, functionally independent potassium transporter(s). Cells deleted for both TRK1 and TRK2 are hypersensitive to low pH; they are severely limited in their ability to take up K+, particularly when faced with a large inward-facing H+ gradient, indicating that the K+ transporter(s) that remains in trk1 delta trk2 delta cells functions differently than those of the TRK class.
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            Author and article information

            Journal
            Microbiology and Molecular Biology Reviews
            Microbiol Mol Biol Rev
            American Society for Microbiology
            1092-2172
            1098-5557
            June 2002
            June 2002
            : 66
            : 2
            : 300-372
            Affiliations
            [1 ]Department of Cell and Molecular Biology/Microbiology, Göteborg University, S-405 30 Göteborg, Sweden
            Article
            10.1128/MMBR.66.2.300-372.2002
            56277d23-44bc-4fd2-ab6c-6c94a32df8b1
            © 2002

            https://journals.asm.org/non-commercial-tdm-license

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