REGULATION OF THE DICTYOSTELIUM GLYCOGEN-PHOSPHORYLASE 2 GENE BY CYCLIC-AMP

A crucial developmental event in the cellular slime mold, Dictyosteliu m discoideum, is glycogen degradation. The enzyme that catalyzes this degradation, glycogen phosphorylase 2 (gp-2), is developmentally regul ated and cAMP appears to be involved in this regulation. We have exami ned several aspects of the cAMP regulation of gp-2. We show that addit ion of exogenous cAMP to aggregation competent amoebae induced the app earance of gp-2 mRNA. The induction of gp-2 mRNA occurred within 1 and 1.5 h after the initial exposure to cAMP. Exposure to exogenous cAMP concentrations as low as 1.0 muM could induce gp-2 mRNA. We also exami ned the molecular mechanism through which cAMP induction of gp-2 occur s. Induction of gp-2 appears to result from a mechanism that does not require intracellular cAMP signaling, and may occur directly through a cAMP binding protein without the requirement of any intracellular sig nalling. We also examined the promoter region of the gp-2 gene for cis -acting elements that are involved in the cAMP regulation of gp-2. A s eries of deletions of the promoter were fused to a luciferase reporter gene and then analyzed for cAMP responsiveness. The results indicated that a region from -258 nucleotides to the transcriptional start site is sufficient for essentially full activity and appears to carry all necessary cis-acting sites for cAMP induction. Further deletion of 58 nucleotides from the 5' end, results in fivefold less activity in the presence of cAMP. Deletion of the next 104 nucleotides eliminates the cAMP response entirely. (C) 1993 Wiley-Liss, Inc.