The cyclic nucleotide phosphodiesterase (phosphodiesterase) plays essential roles throughout the development of Dictyostelium discoideum. It is crucial to cellular aggregation and to postaggregation morphogenesis. The phosphodiesterase gene is transcribed into three mRNAs, containing the same coding sequence connected to different 5' untranslated sequences, that accumulate at different times during the life cycle. A 1.9-kilobase (kb) mRNA is specific for growth, a 2.4-kb mRNA is specific for aggregation, and a 2.2-kb mRNA is specific for late development and is only expressed in prestalk cells. Hybridization of RNA isolated from cells at various stages of development with different upstream regions of the gene indicated separate promoters for each of the three mRNAs. The existence of specific promoters was confirmed by fusing the three putative promoter regions to the chloramphenicol acetyltransferase reporter gene, and the analysis of transformants containing these constructs. The three promoters are scattered within a 4.1-kilobase pair (kbp) region upstream of the initiation codon. The late promoter is proximal to the coding sequence, the growth-specific promoter has an initiation site that is 1.9 kbp upstream of the ATG codon, and the aggregation-specific promoter has an initiation site 3 kbp upstream.When Dictyostelium discoideum amoebae are deprived of nutrients, they initiate a developmental program that results in the formation of a multicellular organism composed of differentiated cell types. The aggregation process that takes place early in development is driven by chemotaxis toward cyclic AMP (cAMP) (6), and one of the earliest events in development is the elaboration of the biochemical apparatus required for chemotaxis toward cAMP (for reviews see references 7, 18, and 23). Soon after starvation, the cells synthesize an adenylate cyclase, a cell surface cAMP receptor, an extracellular phosphodiesterase, and a specific phosphodiesterase inhibitor. These proteins, among others, function coordinately to allow the cells to aggregate by chemotaxis. Cells secrete pulses of cAMP every 5 to 6 min, and neighboring cells respond by moving toward elevated concentrations of cAMP and by emitting cAMP to create a relay. The binding of cAMP to cell surface receptors activates second messenger cascades involving G proteins (27) that lead to a variety of cellular events (for reviews, see references 13 and 20), including the chemotactic response and the regulation of genes specific for development. The cAMP receptor is down regulated and phosphorylated upon constant stimulation by cAMP (25,53), and this results in the adaptation of cellular responses (52). The cyclic nucleotide phosphodiesterase (phosphodiesterase) acts outside the cell to reduce cAMP levels, limiting saturation and down regulation of the receptor. The phosphodiesterase exists in membrane-bound and free extracellular forms (30, 47). Its activity is regulated at the gene level (16) and is controlled at the protein level by a specific inhibitor (15). A m...