The effect of prednisolone injected in vivo on RNA-polymerase activities in isolated rat thymus nuclei.

Abstract

The capacity of isolated rat thymus nuclei to synthesize RNA in vitro was investigated under various experimental conditions. When incubated in the presence of MgCl2 alone thymus nuclei synthesized an RNA product which according to a nearest neighbour frequency analysis contains high proportions of dinucleotide sequences typical for ribosomal precursor RNA: GpC, CpG and GpG. When MgCl2 was replaced in the incubation mixture by MnCl2 and ammonium sulfate the nuclei formed a product of a more DNA‐like nucleotide composition. The time course of the incorporation of tritiated ribonucleosidetriphosphates into acid‐precipitable material was different in the two nuclear polymerase systems: while, in the presence of MgCl2, the incorporation of radioactive AMP or GMP reached a plateau after only 15 min of incubation, the reaction proceeded at a linear rate for at least 40 min in the presence of high concentrations of salt and MnCl2. The absolute amounts of radioactive RNA‐precursor material incorporated into RNA are considerably smaller in the Mg++‐activated system than in the presence of MnCl2 and ammonium sulfate.The administration of prednisolone to adrenalectomized young rats was followed by a decrease in the ability of isolated thymus nuclei to synthesize RNA when MgCl2 was present. The relative frequencies of several dinucleotide pairs in the RNA synthesized by isolated thymus nuclei in the presence of MgCl2 changed significantly in response to steroid treatment. The adminstration of prednisolone, however, did not modify the quantity or the quality of the product formed by thymus nuclei in the Mn++/ammonium sulfate activated reaction. These results further indicate that glucocorticoids exert a preferential inhibitory effect on the formation of ribosomal precursor RNA in rat thymus cells.