Identification of the regulatory subunit of a cAMP-dependent protein kinase in Dictyostelium discoideum

The occurrence of a cytosolic cAMP-binding protein of an approximate molecular weight of 41,000 daltons was monitored in vegetative and developing amoebae of $\text{Dictyostelium}\text{discoideum}$ by the use of the photoaffinity probe (³²P) 8N₃-cAMP. There was a large apparent increase in the amount of this binding protein during development; its molecular weight remained constant, if appropriate methods were employed for the disruption of the amoebae. Comigration during electrophoresis on two-dimensional gels identifies this cAMP-binding protein, photoaffinity-labeled in crude extracts, as the regulatory subunit of the cAMP-dependent protein kinase of $\text{D.}\text{discoideum}$.