Microbiology (1 997), 143,2627-2637 Printed in Great Britain The Sch9 protein kinase in the yeast Saccharomyces cerevisiae controls cAPK activity and is required for nitrogen activation of the f ermenta ble-growth-medium-induced (FGM) pathway Marion Crauwels, Monica C. V. Donaton, Maria Beatriz Pernambuco, Joris Winderickx, Johannes H. de Winde and Johan M. Thevelein Author for correspondence : Johan M. Thevelein. Tel : + 32 16 321507 or 321500. Fax : + 32 16 321979. e-mail : Johan.Thevelein@ bio.ku1euven.ac. be Laboratorium voor Moleculaire Celbiologie, Katholieke Universiteit te Leuven, Kardinaal Mercierlaan 92, B-3001 Leuven-Heverlee, Belgium In cells of the yeast Sacchammyces cerevisiae, trehalase activation, repression of CTTl (catalase), SSA3 (Hsp7O) and other STRE-controlledgenes, feedback inhibition of CAMP synthesis and to some extent induction of ribosomal protein genes is controlled by the Ras-adenylatecyclase pathway and by the fermentable-growth-medium-induced pathway (FGM pathway). When derepressed cells are shifted from a non-fermentable carbon source to glucose, the Ras-adenylate cyclase pathway is transiently activated while the FGM pathway triggers a more lasting activation of the same targets when the cells become glucose-repressed. Activation of the FGM pathway is not mediated by CAMP but requires catalytic activity of CAMP-dependent protein kinase (cAPK; Tpkl, 2 or 3). This study shows that elimination of Sch9, a protein kinase with homology to the catalytic subunits of cAPK, affects all target systems in derepressed cells in a way consistent with higher activity of cAPK in wiwo. In witm measurements with trehalase and kemptide as substrates confirmed that elimination of Sch9 enhances cAPK activity about two- to threefold, in both the absence and presence of CAMP. In wiwo it similarly affected the basal and final level but not the extent of the glucose-induced responses in derepressed cells. The reduction in growth rate caused by deletion of SCHS is unlikely to be responsible for the increase in cAPK activity since reduction of growth rate generally leads to lower cAPK activity in yeast. On the other hand, deletion of SCHS abolished the responses of the protein kinase A targets in glucose- repressed cells. Re-addition of nitrogen to cells starved for nitrogen in the presence of glucose failed to trigger activation of trehalase, caused strongly reduced and aberrant repression of ml and SSA3, and failed to induce the upshift in RPL25 expression. From these results three conclusions can be drawn: (1) Sch9 either directly or indirectly reduces the activity of protein kinase A; (2) Sch9 is not required for glucose-induced activation of the Ras- adenylate cyclase pathway; and (3) Sch9 is required for nitrogen-induced activation of the FGM pathway. The latter indicates that Sch9 might be the target of the FGM pathway rather than cAPK itself. Keywords : yeast, nutrient signalling, trehalase, ribosomal protein genes INTRODUCTION In micro-organisms such as the yeast Saccharomyces cerevisiae nutrients are the prime factors in the en- Abbreviations: cAPK, CAMP-dependent protein kinase; FGM pathway, fermentable-growth-medium-induced pathway. vironment controlling growth, metabolism and devel- opment. In yeast in particular the presence in the growth medium of rapidly fermented sugars such as glucose has dramatic effects on many phenotypic properties. The . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0002-1 578 0 1997 SGM 2627