The capacity of polyadenylated RNA from myogenic cells treated with actinomycin D to direct protein synthesis in a cell-free system.

Cytoplasmic polyadenylated RNA of myogenic cells was shown to decay with biphasic kinetics, suggesting the existence of two main populations of mRNA with respect to stability. In the present study, the stability of mRNA extracted from actinomycin-D-treated cultures of a myogenic cell line was tested by its capacity to direct protein synthesis in the wheat germ cell-free system. The products were analyzed by dodecylsulphate/polyacrylamide gel electrophoresis. All major radioactive bands found in gels used for analyzing the products of the cell-free system directed by polyadenylated RNA extracted from untreated cultures were also found in similar gels containing products of RNA extracted after many hours of application of actinomycin D. The capacity to code for specific protein bands decays with a half-life ranging between 11 and 40 h. No fast-decaying translatable mRNA could be detected by this method. Instead, it was found that during the first 4--6 h following application of actinomycin D, the capacity of RNA to stimulate incorporation of amino acids into total acid-insoluble material increased by 20--30%. The synthesis of specific products increased by up to 100%. The possibility that the fast-decaying polyadenylated RNA or part of it is nontranslatable RNA is discussed.