The RdeA-RegA system, a eukaryotic phospho-relay controlling cAMP breakdown

The regA and rdeA gene products of Dictyostelium are involved in the regula tion of cAMP signaling. The response regulator, RegA, is composed of an N-t erminal receiver domain linked to a C-terminal cAMP-phosphodiesterase domai n. RdeA may be a phospho-transfer protein that supplies phosphates to RegA. We show genetically that phospho-RegA is the activated form of the enzyme in vivo, in that the predicted site of aspartate phosphorylation is require d for full activity. We show biochemically that RdeA and RegA communicate, as evidenced by phospho-transfer between the two proteins in vitro. Phospho -transfer is dependent on the presumed phospho-accepting amino acids, histi dine 65 of RdeA and aspartate 212 of RegA, and occurs in both directions. P hosphorylation of RegA by a heterologous phospho-donor protein activates Re gA phosphodiesterase activity at least 20-fold. Our results suggest that th e histidine phosphotransfer protein, RdeA, and the response regulator, RegA , constitute two essential elements in a eukaryotic His-Asp phospho-relay n etwork that regulates Dictyostelium development and fruiting body maturatio n.