Changes at transcriptional level in the rat liver following whole-body x-irradiation.

Exposure of animals to a single lethal whole-body dose of X-rays is known to cause enhanced rates of protein synthesis in the liver during 12 to 24 hr post-irradiation. Evidence from various lines indicates that these changes are solely the consequence of a general stimulation in RNA synthesis [ 1,2]. Previous studies of ours on the mechanism by which radiation exerts stimulatory effect on RNA biosynthesis in the rat liver have revealed that it is the template capacity of chromatin rather than the level or the activity of RNA polymerase which exhibits distinct rise in the interval between 4 and 24 hr post-irradiation [3]. Several workers have recently reported that under conditions which lead to gene activation specific enhancement in synthesis of certain chromosomal acidic proteins can be discerned in animal cells. Thus in rats, selective stimulation in the synthesis of chromosomal acidic proteins has been observed in the liver following administration of cortisol [4] and glucagon [.5] and in the liver and the uterus in response to estradiol [6]. In this communication, we present evidence to show that concurrent with amplification in template capacity of liver chromatin, incorporation of labelled amino acid precursors into specific chromosomal acidic proteins in the liver is also selectively stimulated during 4 to 24 hr following whole-body exposure of rats to 1000 R X-rays.