Protein kinase activity and ribosome phosphorylation in ethionine-treated rats

The regulation of protein synthesis at the level of the ribosome was investigated using the model system of ethionine-induced inhibition of protein synthesis. The phosphorylation of ribosomal protein S6 was examined in vivo during ethionine intoxication and during the adenine-induced reversal of ethionine intoxication. The extent of phosphorylation of S6 correlated well with protein synthetic activity observed after ethionine, and ethionine followed by adenine treatments. No clear correlation was observed in the ethionine system between cyclic adenosine 3':5'-monophosphate concentration or the activity of ribosomal protein kinase and the phosphorylation of ribosomal protein S6. A role for a cyclic adenosine 3':5'-monophosphate-dependent ribosomal phosphoprotein phosphatase is postulated.