In vivo receptor-mediated phosphorylation of a G protein in Dictyostelium.

Extracellular adenosine 3',5'-monophosphate (cAMP) serves multiple roles in Dictyostelium development, acting as a chemoattractant, a cell-cell signaling molecule, and an inducer of differentiation. The Dictyostelium G-protein alpha subunit G alpha 2 appears to be the major transducer linking the surface cAMP receptor to these intracellular responses. On stimulation of cells with cAMP, G alpha 2 is phosphorylated on one or more serine residues, resulting in an alteration of its electrophoretic mobility. Phosphorylation of G alpha 2 is triggered by increased occupancy of the surface cAMP receptor and is rapid and transient, coinciding with the time course of activation of physiological responses.