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An intersection of the cAMP/PKA and two‐component signal transduction systems in Dictyostelium
Author(s) -
Thomason Peter A.,
Traynor David,
Cavet Guy,
Chang WenTsan,
Harwood Adrian J.,
Kay Robert R.
Publication year - 1998
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/17.10.2838
Subject(s) - biology , phosphodiesterase , signal transduction , protein kinase a , microbiology and biotechnology , phosphorylation , dictyostelium , biochemistry , mutant , protein subunit , gene , enzyme
Terminal differentiation of both stalk and spore cells in Dictyostelium can be triggered by activation of cAMP‐dependent protein kinase (PKA). A screen for mutants where stalk and spore cells mature in isolation produced three genes which may act as negative regulators of PKA: rdeC (encoding the PKA regulatory subunit), regA and rdeA . The biochemical properties of RegA were studied in detail. One domain is a cAMP phosphodiesterase ( K m ∼5 μM); the other is homologous to response regulators (RRs) of two‐component signal transduction systems. It can accept phosphate from acetyl phosphate in a reaction typical of RRs, with transfer dependent on Asp212, the predicted phosphoacceptor. RegA phosphodiesterase activity is stimulated up to 8‐fold by the phosphodonor phosphoramidate, with stimulation again dependent on Asp212. This indicates that phosphorylation of the RR domain activates the phosphodiesterase domain. Overexpression of the RR domain in wild‐type cells phenocopies a regA null. We interpret this dominant‐negative effect as due to a diversion of the normal flow of phosphates from RegA, thus preventing its activation. Mutation of rdeA is known to produce elevated cAMP levels. We propose that cAMP breakdown is controlled by a phosphorelay system which activates RegA, and may include RdeA. Cell maturation should be triggered when this system is inhibited.