Regulation of guanylyl cyclase by a cGMP-binding protein during chemotaxis in Dictyostelium discoideum

Chemoattractants transiently activate guanylyl cy-clase in Dictyostelium discoideum cells. Mutant analysis demonstrates that the produced cGMP plays an essen-tial role in chemotactic signal transduction, controlling the actomyosin-dependent motive force. Guanylyl cy-clase activity is associated with the particulate fraction of a cell homogenate. The addition of the cytosol stimu-lates guanylyl cyclase activity, whereas the cytosol plus ATP/Mg21 inhibits enzyme activity. We have analyzed the regulation of guanylyl cyclase in chemotactic mu-tants and present evidence that a cGMP-binding protein mediates both stimulation and ATP-dependent inhibi-tion of guanylyl cyclase. Upon chromatography of cytosolic proteins, cGMP binding activity co-elutes with both guanylyl cyclase