GLUCOSE EXERTS OPPOSITE EFFECTS ON MESSENGER-RNA VERSUS PROTEIN AND ACTIVITY LEVELS OF PDE1, THE LOW-AFFINITY CAMP-PHOSPHODIESTERASE FROM BUDDING YEAST, SACCHAROMYCES-CEREVISIAE

In budding yeast (Saccharomyces cerevisiae), a low-affinity phosphodie sterase, Pde1, and a high-affinity phosphodiesterase, Pde2, are respon sible for the degradation of cAMP. Addition of glucose to glycerol-gro wn yeast cells is known to cause a transient increase in the cAMP leve l and recent work has indicated a specific involvement of Pde1 in this response, In this work me show that glucose addition induces the accu mulation to high levels of mRNA encoding Pde1. This increase continues for at least 8 hours and is due to enhanced transcription of the PDE1 gene, since glucose addition does not change the stability of the Pde 1 mRNA. Surprisingly, using an assay method specific for Pde1, we obse rved that the activity of Pde1 remains constant and finally decreases several-fold during the same period, In addition, this activity profil e closely follows the Pde1 protein level as judged from Western blotti ng with antibodies directed against Pde1. Experiments using cyclohexim ide, a general inhibitor of translation, allow to exclude the possibil ity of a futile cycle of Pde1 synthesis and degradation. Hence, glucos e addition appears to trigger an increase in PDE1 gene transcription t ogether with a specific inhibition of the translation of Pde1 mRNA. (C ) 1997 Federation of European Biochemical Societies.