Protein kinase A is a positive regulator of spore coat gene transcription in Dictyostelium.

The cotA, cotB, and cotC genes encode the major spore coat proteins of Dictyostelium. All three cot genes are coordinately expressed as aggregation is nearing completion. Induction and maintenance of their expression is dependent upon the presence of extracellular cAMP. We show that expression of a dominant inhibitor of the cAMP dependent protein kinase (PKA) in prespore cells greatly reduces the transcription rates of the cotB and cotC genes. All three cot genes contain, in their upstream regulatory regions, short sequence elements that have a high content of cytosine and adenosine residues. These CA-rich sequences are essential for optimal cot gene transcription. We show that expression of the dominant PKA inhibitor results in a greatly reduced level of the binding activity that recognizes the CA-rich sequences upstream of the cotB gene. Thus PKA acts, either directly or indirectly, to control expression of the cot genes and it may do so by modulating the activity of a DNA binding protein. However, we find that mutant cells where PKA is constitutively active still require exogenous cAMP for optimal cot gene expression in dissociated cells, suggesting that a separate, PKA-independent, signalling pathway is also involved in the regulation of cot gene expression by extracellular cAMP.