Abstract
Rate of the incorporation of 3H-orotic acid into two rapidly labelled RNA fractions, pH 7.6 RNA and pH 8.3 RNA fractions, of liver nuclei was examined in rats received whole-body X-irradiation of 650 R. Rate of the incorporation showed an increase immediately after irradiation, and a decrease during the succeeding four days, and then returned to the control levels. Degree of decrease in the incorporation by X-irradiation was greater in the pH 7.6 RNA fraction than in the pH 8.3 RNA fraction. Sucrose density gradient analysis revealed that there was a minor modification of sedimentation profile of pH 7.6 RNA while no change was detected in pH 8.3 RNA, at one day after X-irradiation. The incorporation of 3H-orotic acid into the acid-soluble fraction of whole liver cells did not change significantly. Free pyrimidine nucleotides in the acidsoluble fraction increased at one day after irradiation. This may explain, at least in part, the decreased rate of the incorporation of 3H-orotic acid into the nuclear RNA fractions at this period.
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