Radiation-induced fluctuation of the polysome content in adequately oxygenated tetrahymena pyriformis.

The polysome content of the ciliate protozoan Tetrahymena pyriformis is transiently reduced by gamma-irradiation. In order to test whether this is a result of a respiration-produced or radiation-produced hypoxia or some other mechanism, the oxygen content of the culture was determined during and after irradiation, and the polysome contents and rates of amino acid incorporation were measured with and without air bubbling. Irradiation (40 krad at approximately 3 krad/min) produced approximately a 25 per cent loss in dissolved O2 content in the medium. This decrease is not sufficient to affect the polysome level, since (a) the same radiation-induced loss of polysomes and inhibiition of amino acid incorporation was observed whether or not the culture was bubbled with air during the irradiation and (b) bubbling unirradiated cultures with gas mixtures containing as little as 17 per cent of the normal O2 content did not influence the polysome level. As long as the cells are irradiated as a shallow layer in open flasks, replacement of O2 from the gas phase appears adequate, and neither respiration-induced nor radiation-induced hypoxia masks the effects of the radiation.

Selective inhibition of precursor incorporation into ribosomal RNA in gamma-irradiated Tetrahymena pyriformis.

Sublethal doses of gamma radiation are known to inhibit total RNA synthesis in the ciliate protozoan Tetrahymena. To determine if the synthesis of a particular class of RNA is preferentially inhibited, pulse-labeled RNA was isolated from normal exponentially growing cells, irradiated cells, and cells in which total RNA synthesis had recovered to the pre-irradiation level. The RNAs were analyzed by SDS-polyacrylamide gel electrophoresis and oligo(dT)-cellulose column chromatography. Inhibition of RNA synthesis primarily involves ribosomal RNA. However, radiation does not cause a delay in the processing of precursor rRNA or a preferential loss of either of the mature rRNAs. Following irradiation, poly(A)-containing RNA [poly(A+)RNA] is synthesized at a rate up to three times greater than the control rate. The elevated poly(A+)RNA synthesis occurs during the period of depressed rRNA synthesis and even after rRNA synthesis has recovered to its pre-irradiation rate. While the sizes of the total cellular ribonucleoside triphosphate pools are depressed in the irradiated cells, these pools probably do not represent the actual compartments containing the precursors for RNA synthesis, and the observed changes cannot explain the modifications in macromolecular synthesis in irradiated Tetrahymena.

Radiation-induced inhibition of RNA synthesis in Tetrahymena pyriformis.

Radiation-induced disturbances in RNA synthesis were investigated in exponentially growing Tetrahymena. Sub-lethal doses of gamma-radiation lead to a transient, dose-dependent decrease in the rate of total RNA synthesis measured by 3H-uridine incorporation, without an alteration of 3H-uridine uptake by the cells. The rate of 3H-uridine incorporation decreases exponentially with dose. In contrast, the duration of inhibition of RNA synthesis is linearly dependent on dose. Target-theory calculations suggest that the sensitive molecule has a molecular weight of about 2 X 10(7) Daltons.

Nuclear-cytoplasmic relations in the mitosis of sea urchin eggs. 3. Gamma-ray--induced damage to whole eggs and nucleate and anucleate half-eggs.

Sea urchin eggs were cut into halves. The nucleate and anucleate halves and whole eggs were irradiated with gamma-rays and then fertilized with normal sperm. The first mitosis of the diploid half-egg was more delayed than the division of the whole egg. There was a small, but highly significant, delay of the mitosis of the haploid half-egg, thus demonstrating cytoplasmic sensitivity to ionizing radiation. Since the sensitivity of nucleate cells is influenced by cytoplasmic volume, the problem of the role of cytoplasm in repair is considered in relation to these data and other reports in the literature.