Stimulation of synthesis of DNA-like and ribosomal RNA by growth hormone

Abstract

Rapidly labelled RNA isolated from liver nuclei of rats given pulses of [ 3H]orotic acid were separated into four fractions by chromatography on methyl albumin kieselguhr columns. One fraction (Q1) was shown to be ribosomal-like RNA, for its labelling was inhibited by low doses of actinomycin and cycloheximide, it had a high G + C composition, and was methylated. Two other fractions (Q2 and TD RNA) were of lower G + C composition than Q1, their labelling was not inhibited by actinomycin and cycloheximide, and they were heterodisperse and of high molecular weight. Hypophysectomy of rats depressed the rate of labelling of Q1 RNA but did not affect the labelling of Q2 and TD RNA. Treatment of rats with growth hormone was first followed by stimulation of labelling of the Q1 RNA, then by increased labelling of Q1, Q2 and TD RNA and, finally, after 18 hours, preferentially stimulated labelling of Q2 and TD RNA fractions. It is concluded that growth hormone treatment first results in stimulation of synthesis of ribosomal RNA and, later, of DNA-like RNA.