REGULATION OF TRANSCRIPTION IN RAT THYMUS-CELLS BY GLUCOCORTICOIDS

Treatment of rat thymus cells with glucocorticoids resulted in the transient stimulation of RNA polymerase B activity within 10 min of steroid addition. This early effect was followed by the inhibition of both RNA polymerase A and B activities. The inhibitory effect of glucocorticoids on RNA polymerase A activity, but not that on RNA polymerase B activity, was abolished by prior treatment of the cells with inhibitors of mRNA and protein synthesis, and by glucose deprivation. It is concluded that the inhibitory action of glucocorticoids on RNA polymerase A activity is mediated by a steroid-induced regulatory protein, but that the effect on RNA polymerase B activity represents a direct action of the steroid-receptor complex on the structure of chromatin. Dual-labelling techniques, followed by SDS-polyacrylanude disc gel electrophoresis, have been used to search for glucocorticoid-induced proteins. Evidence has been obtained for the steroid-mediated synthesis of at least three non-histone chromosomal proteins, with apparent molecular weights of 39,000, 20,000 and 18,000. © 1979.