The regulation of enzyme synthesis by steroid hormones: The role of translation

Following a single injection of hydrocortisone into adrenalectomized rats, the levels of tryptophan pyrrolase and tyrosine transaminase in the liver first rise and then decrease to their basal levels. Although actinomycin D blocks the initial steroid-induced increase, later administration of the antibiotic (or of 5-fluorouracil) causes an increase in the levels of these enzymes. A mechanism is proposed to account for the late response to inhibitors of RNA synthesis in which a “cytoplasmic repressor” can inhibit the translation of the messenger RNA's corresponding to tryptophan pyrrolase and tyrosine transaminase. Cytoplasmic repression is postulated to depend on continued RNA and protein synthesis, and the “repressor” is thought to have a rapid rate of turnover.