DEVELOPMENTAL AND CAMP-MEDIATED REGULATION OF GLYCOGEN-PHOSPHORYLASE-1 IN DICTYOSTELIUM-DISCOIDEUM

The Dictyostelium discoideum glycogen phosphorylase-1 (gp-1) exhibits a complex pattern of developmental expression in which differential te mporal regulation of enzyme activity, protein levels and mRNA levels i s observed. This pattern of expression implies that gp-1 regulation oc curs at multiple levels, probably involving both transcriptional and p ost-transcriptional events. Post-translational control of gp-1 activit y, in effect, actually regulates the protein from a developmental pers pective. In this report we have examined several facets of this regula tion. We show that addition of exogenous cAMP to cells in suspension c ulture caused changes in gp-1 enzyme activity and mRNA levels that are identical to those observed during normal development, suggesting tha t cAMP is involved in the regulation of gp-1. Exogenous cAMP could reg ulate gp-1 mRNA expression at concentrations as low as 1.0 mu M. cAMP regulation of gp-1 mRNA appeared to occur through a mechanism that req uired intracellular cAMP signalling. We identified regions of the prom oter necessary for gp-1 expression by using gp-1 promoter deletions to drive the expression of a luciferase reporter gene. Results of these experiments suggested that developmental and cAMP-mediated changes in gp-1 mRNA levels were the result of alterations in transcription. The promoter analysis also suggested that a vegetative specific element is located between - 785 and -1894 nucleotides from the transcriptional start site. Elements necessary for maximal developmental and cAMP-medi ated expression appear to be located between -1153 and -1894 nucleotid es from the cap site. Sequence elements located between -180 and -1153 appear to be required for a basal level of late developmental express ion.