MAK column chromatography of RNA extracted from synchronized Tetrahymena after X-irradiation revealed age-dependent depressions in the cellular content of the various species of RNA and in the synthesis of${\rm Q}_{1},\ {\rm Q}_{2}$, and TD RNA. Sucrose density-gradient analysis of polyribosomes extracted from irradiated cells revealed age-dependent depressions of cellular polyribosomes, of newly synthesized messenger RNA, and of nascent polypeptide synthesis. The results are interpreted as supporting the hypothesis that the radiation-induced delay of cell division may be due primarily to the radiation-induced depression of division-essential messenger RNA synthesis.

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