Effect of growth hormone on ribonucleic acid metabolism. 3. Nature and characteristics of nuclear subfractions stimulated by hormone treatment

Abstract

Growth hormone stimulates the incorporation in vivo of [P32]orthophosphate and [6-C14]orotic acid into rat-liver RNA. The initial stimulation occurs in the nuclear fractions of RNA, but with longer incorporation times the microsomal fractions of RNA also become highly labelled. The administration of growth hormone increases particularly the specific radioactivity of the nucleolar RNA fraction. This stimulation is inhibited by actinomycin D. The molar base ratios of these fractions in liver nuclei from normal and growth-hormone-treated rats have been determined. The hormone does not cause any qualitative change in the N-2 subtraction (RNA extracted with DNA-proteins in 1 M-sodium chloride), but the base composition of the heterogeneous polydisperse nucleolar RNA is altered. It is suggested that the hormone may primarily stimulate the synthesis of ribosomal RNA and messenger RNA.