The effect of X-radiation on the incorporation of 14C-orotic acid into rapidly labeled nuclear and cytoplasmic RNA

Abstract

The effects of X-radiation on 14C-orotic acid incorporation into nuclear and cytoplasmic rat liver RNA were studied in animals killed 24 hr after partial hepatectomy. The animals received total-body doses of 1500 R and were injected with orotic acid 10, 20, 40 and 60 min prior to sacrifice. X-radiation inhibits the incorporation of orotic acid into nuclear and cytoplasmic RNA in the livers of animals injected with the precursor 10 or 20 min before they are killed. Sixty minutes after orotic acid injection no inhibition of the labeling of nuclear and cytoplasmic RNA was observed. The results suggest that X-radiation retards the incorporation of 14C-orotic acid into the rapidly labeled nuclear and cytoplasmic RNA and that in the cytoplasm X-radiation preferentially interferes with the labeling of RNA with rapid turnover. The retardation of the incorporation of 14C-orotic acid into nuclear RNA can be detected 1 hr after irradiation and reaches a maximum at 6 hr. It is possible that the primary injury produced by X-radiation involves the DNA molecules which at the time of the irradiation function as template for the synthesis of rapidly labeled RNA.