Actinomycin D and the regulation of enzyme biosynthesis during development of Dictyostelium discoideum

Actinomycin D, when added to differentiating Dictyostelium discoideum cells, completely inhibits synthesis of ribosomal RNA but only partially inhibits synthesis of mRNA. Hence, earlier experiments using this drug, which indicated that the period of synthesis of mRNAs for several developmentally regulated enzymes preceded the period of translation by several hours, must be re-evaluated. We show here that a combination of actinomycin D and daunomycin does rapidly inhibit synthesis of mRNA; also there is a rapid and complete inhibition of biosynthesis of the three developmentally regulated enzymes studied. One interpretation of these results is that translation of mRNA follows closely upon synthesis of the mRNA, and that the primary control of protein biosynthesis during Dictyostelium development is at the level of mRNA transcription.