Macromolecular Synthesis and Cell Division in X-Irradiated Tetrahymena

The sensitivity of heat-synchronized Tetrahymena pyriformis to x-radiation was dependent upon the magnitude of the radiation dose and the age of the cell population. Division delays of increasing duration were exhibited by cells irradiated with progressively greater doses of x-radiation at a specific time during the cell cycle. Moreover, division delays of increasing duration were produced when cells were irradiated with a specific dose at progressively later times during the cell cycle. The precise time of transition from radiation sensitivity to radiation insensitivity was found to be dose dependent. Studies involving the addition of either actinomycin D or puromycin to cells at various times after irradiation indicated that both RNA and protein synthesis were required for the recovery of Tetrahymena from the radiation effects; cell division was employed as an index for recovery from radiation damage. DNA, RNA, and protein synthesis in irradiated cells were all differentially depressed. These results are discussed in terms of their relationship to the radiation-induced delay of cell division.