Nucleoprotein Changes in Regenerating Liver Nuclei after X-irradiation

Summary

800 r whole-body irradiation was given to rats 24 hours after partial hepatectomy, and two aspects of the response of the liver nuclei were studied in the period 24–48 hours after hepatectomy. Firstly the in vivo incorporation-rate of DNA and protein precursors, and secondly the absolute amount of protein and DNA in the nucleus at various times after hepatectomy and irradiation.

Incorporation of tritiated thymidine into liver DNA was found to be significantly inhibited during the whole period in irradiated animals. Incorporation of ¹⁴C-lysine into acid-insoluble protein of liver nuclei was similarly inhibited during most of this period. In contrast there was apparently no inhibition of incorporation of ¹⁴C-lysine into histone after irradiation.

Following the first wave of cell-division which occurs in regenerating liver at about 28 hours after partial hepatectomy, all three components of the nucleus approximately double in amount before the next cell-division. After irradiation, however, this increase does not occur for the DNA and acid-insoluble protein components. The amount of histone however, increases in the nucleus to the same extent after irradiation as it does in the liver nuclei of non-irradiated animals.

The net result of these processes is that the amount of protein, particularly histone, relative to DNA in the nucleus is increased after irradiation with the result that the composition of the irradiated nucleus differs markedly from that of the non-irradiated.