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In an attempt to understand the molecular mechanism underlying the depressive effect of glucocorticoids on corticotropin production, the level of corticotropin messenger RNA activity in rat pituitaries was measured with the use of the cell-free protein-synthesizing system derived from wheat germ. The large translation product of corticotropin messenger RNA was identified and quantitated by indirect immunoprecipitation with antibody against corticotropin. The level of corticotropin messenger RNA activity was increased 3- to 6-fold by adrenalectomy. Dexamethasone administration to adrenalectomized rats resulted in a marked suppression of corticotropin messenger RNA activity. Cortisol and corticosterone also exhibited a suppressive effect but were less effective than dexamethasone. In contrast, nonglucocorticoids such as progesterone and aldosterone had no suppressive effect. These results indicate that at least part of the glucocorticoid effect on corticotropin production in the pituitary is exerted at the pretranslational level.

Total RNAs extracted from amnion, chorion and decidua of the human second trimester placentas were translated in the cell-free translation system, followed by immunoprecipitation with antiserum to human prolactin (Prl) and electrophoresis in sodium dodecyl sulfate slab gel. A single immunospecific protein with an apparent molecular weight of approximately 25,500, about 3000 daltons larger than authentic Prl, was formed only with RNA from decidua, and it competed with unlabeled Prl but not with unlabeled human placental lactogen (hPL) for binding to the antibody. The electrophoretic patterns of the fragments formed by partial enzymatic proteolysis of it and authentic Prl were similar.

Polyadenylate-containing RNA prepared from the membrane fraction of bovine anterior pituitary gland was shown to direct the synthesis of a large translation product related to corticotropin (adrenocorticotropic hormone) in a cell-free system derived from wheat germ. This product was identified by immunoprecipitation with specific antibody against corticotropin, followed by electrophoretic analysis of the dissociated immunoprecipitate on sodium dodecyl sulfate-polyacrylamide gel. Further evidence for the identity of the translation product was provided by the presence of a common peptide in the chymotryptic digest of [35S]methionine-labeled cell-free product and in that of authentic corticotropin. The molecular weight of the translation product was estimated to be approximately 35,000, based on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These results indicate that corticotropin messenger RNA directs the cell-free synthesis of a product that contains the amino acid sequence of corticotropin but is much larger than this hormone.

The distribution of the mRNA coding for the common precursor of corticotropin and beta-lipotropin among different parts of the bovine pituitary has been investigated by quantifying the mRNA activity with the use of a cell-free protein-synthesizing system. The results obtained have demonstrated that this mRNA activity is located both in the anterior lobe and in the intermediate lobe, while it is essentially not detectable in the neural lobe nor in the stalk. The structural identity of the translation products of corticotropin/beta-lipotropin mRNA from the anterior and from the intermediate lobe has been indicated by their molecular weight as well as by the electrophoretic patterns of the peptide fragments formed from them upon partial enzymatic proteolysis or upon cyanogen bromide cleavage. The specific activity of corticotropin/beta-lipotropin mRNA in the intermediate lobe is about 20-fold higher than that in the anterior lobe, and the total activity of this mRNA in the former is about 2-fold higher than that in the latter. In the intermediate lobe, the translation product of corticotropin/beta-lipotropin mRNA amounts to almost one-third of the products encoded by total translatable mRNA. These results indicate that corticotropin/beta-lipotropin mRNA represents a major mRNA species in intermediate lobe of the pituitary, thus suggesting that this lobe may perform a highly specialized function in producing a large amount of the common precursor of corticotropin and beta-lipotropin.