CAMP INHIBITS BUD GROWTH IN A YEAST-STRAIN COMPROMISED FOR CA2+ INFLUX INTO THE GOLGI

Biochemical and physiological studies have implicated cAMP and cAMP-de pendent protein kinase (PKA) in a plethora of essential cellular proce sses. Here we show that yeast cells partially depleted of PKA activity (due to a tpk(w) mutation) and bearing a lesion in a Golgi-localized Ca2+ pump (Pmr1), arrest division with a small bud. The bud morphology of the arrested tpk1(w) pmr1 mutant cells is characteristic of cells in S phase; however, the terminal phenotype of processes such as DNA r eplication and nuclear division suggests Is arrest al the G2/M boundar y. This sma!! bud, G2-arrest phenotype is similar tb that of strains w ith a defect in cell wall biosynthesis (pkc1) or membrane biogenesis ( och1); however, the biochemical defect may re different since the tpk1 (w) pmr1 double mutants retain viability. the growth defect of the tpk 1(w) pmr1 mutant can be alleviated by preventing the increase in cellu lar,cAMP levels thai is known to be associated with a decrease in PKA activity, or by supplementing the medium with millimolar amounts of Ca 2+. Although the biochemical consequences of Il-iis increase in cAMP c oncentration are not known, the small-bud phenotype of ?he double muta nt and the known protein processing defect of lhc pmr1 lesion suggest that the localization or function of some membrane component might be compromised and susceptible to perturbations in cellular cAMP levels. One candidate for such a protein is the cAMP-binding membrane ectoprot ein recently described in yeast.