Glucocorticoids directly affect the synthesis of ribosomal RNA in rat-liver cells.

Administration of the glucocorticoid dexamethasone to rats significantly stimulated the synthesis of ribosomal RNA by hepatic nuclei in vitro, as determined by hybridization to plasmid DNA containing the appropriate gene from X. laevis. This effect was also seen in rats in which RNA polymerase B had previously been blocked by the administration of alpha-amanitin. RNA synthesized in response to the hormone hybridized to both the 5' and 3' end of the gene for the precursor to ribosomal RNA. We conclude from these data that the steroid directly affects transcription of the ribosomal gene without obligatory participation of RNA polymerase B and hence the intermittent production of mRNA or its translation products.