EFFECT OF AGING AND GAMMA-RADIATION ON ACETYLATION OF RAT-LIVER HISTONES

We studied age-related and radiation induced changes in histone acetyl transferase activity and acetylation of histone fractions in normal an d regenerating rat livers. Male Wistar rats aged 1-28 months were used through the studies. They were exposed to whole-body doses of 5.7 Gy gamma radiation from a Co-60 source and partial hepatectomy was carrie d out 30 min after irradiation. Within nuclei isolated from normal and regenerating livers of rats, acetyltransferase activity of histones i ncreased with age. An age-dependent decrease in histone acetyltransfer ase activity in normal and regenerating rat livers was also obvious at the time of maximum activity (i.e. at the 4th min of incubation). The radiation-induced drop in acetyltransferase activity was mild in norm al livers. Twenty-four hours after partial hepatectomy, acetyltransfer ase activity in regenerating fivers was almost completely inhibited by irradiation. The acetylation of histone fractions and subfractions wa s not equal. The highest activity among all histone fractions was foun d in fraction H4. In regenerating livers of non-irradiated and irradia ted rats, there was a greater rate of acetylation in tetraacetylated s ubfractions of histone H4 compared with intact livers.