Effects of hydrocortisone upon metabolism of histones in rat liver

Abstract

1. 1. Synthesis of DNA-like nuclear RNA is stimulated in livers of adrenalectomised rats within an hour of intraperitoneal administration of hydrocortisone, although incorporation of [¹⁴C]lysine into total histones is unaffected within this period. 2. 2. Rat-liver DNA and histones have been found to have approximately the same turnover rates as measured by following the decrease in specific activities after pre-labelling with [Me-³H]thymidine and uniformly labelled l-[¹⁴C]lysine. In the first 15 days, the half-life times of labelled DNA and histones are 7.2 and 6.5 days, respectively, and in the subsequent 15-35 days, 33.1 and 27.2 days, respectively. 3. 3. Adrenalectomy does not alter these decay rates, nor does repeated injection of hydrocortisone to adrenalectomised rats cause any deviation in the decay patterns. 4. 4. Hydrocortisone stimulates incorporation in vivo of [³²P]orthophosphate into both the lysine-rich and arginine-rich histone fractions of rat-liver nuclei, the stimulation in the former fraction being much greater than that in the latter. 5. 5. Actinomycin D has no effect on the hydrocortisone-induced increase in phosphorylation of histones although it considerably suppresses synthesis of DNA-like nuclear RNA.