Yeast Genetics and Molecular Biology 2000
University of Washington
Seattle, Washington USA
July 2000

Name: Geyskens, Ilse
Mailing Address: Molecular Cell Biology, Katholieke Universiteit Leuven, K.Mercierlaan 92, Heverlee, 3001, Belgium
Email Address: ilse.geyskens@bio.kuleuven.ac.be
Phone & FAX numbers: +3216321512 & +3216321979

#127"

Domain structure and subcellular localisation of the Sch9 protein kinase.
Ilse Geyskens, Jan C.T. Bergsma, Shantha H.M.C. Kumara, Johan M. Thevelein, Stefaan Wera
Molecular Cell Biology, Katholieke Universiteit Leuven, K.Mercierlaan 92, Heverlee, 3001, Belgium

The Sch9 protein kinase plays an important role in nitrogen induction of the fermentable-growth-medium-induced (FGM) signalling pathway. Deletion of SCH9 causes slow growth, prevents FGM-induced activation of trehalase and delays FGM-induced repression of STRE-controlled genes. The catalytic domain and the C-terminus of Sch9 are highly homologous to mammalian protein kinase B (PKB) and PKB expression partially restored the sch9 deletion phenotype. Mammalian PKB contains a PH (pleckstrin homology) domain able to bind PtdIns(3,4,5)P3and PtdIns(3,4)P2. Sch9, on the other hand, does not have a PH-domain but contains a C2-domain. C2-domains are known to bind phospholipids. Using co-immunoprecipitation experiments, we show that intact Sch9, as well as its isolated C2-domain, interact with vesicles containing phosphatidylcholine/phosphatidylserine. We also show that during growth on glucose containing medium the Sch9 protein kinase is located exclusively at the membrane. Overexpression of the isolated C2-domain in wild type cells mimics the slow growth phenotype of an sch9 deletion strain, indicating that the C2-domain might have a regulatory effect besides its function in targetting Sch9 to the membrane.

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