Detection and developmental regulation of the mRNA for the regulatory subunit of the cAMP-dependent protein kinase of D. discoideum by cell-free translation.

cAMP is an important effector of the development of Dictyostelium discoideum amoebae and could exert its effects on gene expression through the cytosolic cAMP-dependent protein kinase (cAK). Antibodies, specific for the regulatory subunit (R) of the cAK, were used to investigate the developmental regulation of the corresponding mRNA (R-mRNA) by in vitro translation and immunoprecipitation. Under such conditions, a single polypeptide of the same mol. wt. as R (42 kd) is detected, showing that the protein is not synthesized as a large precursor. The level of the R-mRNA, which is low in vegetative cells, increases 10- to 20-fold during the first hours of development. Its expression is stimulated by the treatment of AX3 cells with cAMP either added to a concentration of 1 mM or given as 0.1 microM pulses every 5 min, whereas such treatments have little or no effect in cells of strain AX2. The R-mRNA remains highly expressed (0.01-0.03% of translatable mRNA) throughout post-aggregative development; it is not affected by mechanical disaggregation of the multicellular organism. The parallel developmental time courses of the translatable R-mRNA and the R protein produced in vivo suggest that the expression of this polypeptide is regulated at the level of mRNA synthesis.