THE PDE2 GENE OF SACCHAROMYCES-CEREVISIAE IS ALLELIC TO RCA1 AND ENCODES A PHOSPHODIESTERASE WHICH PROTECTS THE CELL FROM EXTRACELLULAR CAMP

The high affinity cAMP phosphodiesterase, encoded by PDE2, is an impor tant component of the cAMP-dependent protein kinase signaling system i n Saccharomyces cerevisiae. An unexpected phenotype of pde2 mutants is sensitivity to external cAMP. This trait has been found independently for real mutants and has been used to monitor the effects of cAMP on several biological processes. We demonstrate here that RCA1 is identic al to PDE2. Further analysis of the phenotype of pde2 deletions reveal that exogenously added cAMP results in an increase in the internal le vel of cAMP. This increase slows down the rate of cell division by inc reasing the length of the G1 phase of the cell cycle and leads to incr eased cell volume. Also, cells with a disrupted PDE2 gene previously a rrested by nutrient starvation rapidly lose thermotolerance when incub ated with exogenous cAMP. From these observations we propose that a ro le of the PDE2-encoded phosphodiesterase may be to help insulate the i nternal cAMP pools from the external environment. This protective role might also be important in other eukaryotic organisms where cAMP is a key second messenger.