Molecular cloning and developmental expression of the cyclic nucleotide phosphodiesterase gene of Dictyostelium discoideum

The cyclic nucleotide phosphodiesterase of Dictyostelium discoideum functions to maintain the responsiveness of cells to the chemoattractant cAMP during the aggregation phase of development. We have prepared a cDNA library and have isolated clones which contain a portion of the 5' untranslated region and the entire coding and 3' untranslated portions of the cyclic nucleotide phosphodiesterase gene. The primary structure of the extracellular cyclic nucleotide phosphodiesterase precursor has been deduced from the nucleotide sequence. The molecule is composed of 452 amino acids and was calculated to have a molecular mass of 51,078 daltons. Forty-nine amino-terminal residues which contain a hydrophobic leader sequence are not present in the mature extracellular enzyme. Four potential asparagine-linked glycosylation sites were found within the phosphodiesterase. An amino acid sequence homology search revealed no closely related proteins. Phosphodiesterase mRNA levels are low in growing cells and first increase soon after the onset of development. The amount of transcript then decreases before rising in abundance to maximum levels during the terminal stages of cell aggregation and apical tip formation. During formation of the fruiting body, levels of phosphodiesterase mRNA decrease. Exposure of cells to cAMP increases the amount of phosphodiesterase mRNA. Increases of mRNA abundance are correlated with increases in enzyme activity, suggesting regulation at the level of transcription.