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Involvement of distinct G‐proteins, Gpa2 and Ras, in glucose‐ and intracellular acidification‐induced cAMP signalling in the yeast Saccharomyces cerevisiae

Sonia Colombo, Pingsheng Ma, Liesbet Cauwenberg, Joris Winderickx, Marion Crauwels, Aloys Teunissen, David Nauwelaers, Johannes H. de Winde, Marie‐Françoise Gorwa, Didier Colavizza, Johan M. Thevelein

Author Affiliations

  1. Sonia Colombo1,
  2. Pingsheng Ma1,
  3. Liesbet Cauwenberg1,
  4. Joris Winderickx1,
  5. Marion Crauwels1,
  6. Aloys Teunissen1,
  7. David Nauwelaers1,
  8. Johannes H. de Winde2,
  9. Marie‐Françoise Gorwa3,
  10. Didier Colavizza3 and
  11. Johan M. Thevelein*,1
  1. 1 Laboratorium voor Moleculaire Celbiologie, Katholieke Universiteit Leuven, Kardinaal Mercierlaan 92, B‐3001, Leuven‐Heverlee, Flanders, Belgium
  2. 2 Institut für Mikrobiologie und Genetik, Technische Hochschule Darmstadt, Schnittspahnstrasse 10, D‐64287, Darmstadt, Germany
  3. 3 Lesaffre Développement S.A., Rue Gabriel Péri 147, BP 6027, F‐59706, Marcq‐en‐Baroeul, Cedex, France
  1. *Corresponding author. E-mail: johan.thevelein{at}bio.kuleuven.ac.be
  1. S.Colombo and P.Ma contributed equally to this work

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Abstract

Adenylate cyclase activity in Saccharomyces cerevisiae is dependent on Ras proteins. Both addition of glucose to glucose‐deprived (derepressed) cells and intracellular acidification trigger an increase in the cAMP level in vivo. We show that intracellular acidification, but not glucose, causes an increase in the GTP/GDP ratio on the Ras proteins independent of Cdc25 and Sdc25. Deletion of the GTPase‐activating proteins Ira1 and Ira2, or expression of the RAS2val19 allele, causes an enhanced GTP/GDP basal ratio and abolishes the intracellular acidification‐induced increase. In the ira1Δ ira2Δ strain, intracellular acidification still triggers a cAMP increase. Glucose also did not cause an increase in the GTP/GDP ratio in a strain with reduced feedback inhibition of cAMP synthesis. Further investigation indicated that feedback inhibition by cAPK on cAMP synthesis acts independently of changes in the GTP/GDP ratio on Ras. Stimulation by glucose was dependent on the Gα‐protein Gpa2, whose deletion confers the typical phenotype associated with a reduced cAMP level: higher heat resistance, a higher level of trehalose and glycogen and elevated expression of STRE‐controlled genes. However, the typical fluctuation in these characteristics during diauxic growth on glucose was still present. Overexpression of Ras2val19 inhibited both the acidification‐ and glucose‐induced cAMP increase even in a protein kinase A‐attenuated strain. Our results suggest that intracellular acidification stimulates cAMP synthesis in vivo at least through activation of the Ras proteins, while glucose acts through the Gpa2 protein. Interaction of Ras2val19 with adenylate cyclase apparently prevents its activation by both agonists.

  • Received February 20, 1998.
  • Revision received April 8, 1998.
  • Accepted April 9, 1998.
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