Isolation of mRNA from bovine pituitary. The cell-free synthesis of the alpha and beta subunits of luteinizing hormone.

RNA derived from bovine steer pituitary was translated in wheat germ cell-free extracts containing [35S]methionine. Antisera generated against purified denatured alpha and beta subunits of lutropin were used to demonstrate the synthesis of both proteins in vitro. The immunoprecipitated products of the cell-free system were resolved on sodium dodecyl sulfate/polyacrylamide gels and it was observed that the molecular weight of the immunoprecipitated alpha subunit protein was approximately 14,000, while that of the beta protein was estimated to be 16,000. Since the molecular weights of authentic alpha and beta subunits are 10,600 and 14,000 respectively, the cell-free products presumably represented their pre-protein forms. The ratio of the immunoprecipitated subunit pre-proteins was dependent on the magnesium concentration in the translation mixtures; at 2.1 mM, translation of lutropin alpha and beta mRNAs was comparable. RNA isolated from cow pituitary tissue directed the synthesis of fivefold less of the alpha and beta immunoprecipitated proteins than did steer RNA. Since the blood levels of gonadal steroids are higher in the cow, the results supported the hypothesis that lutropin alpha and beta mRNA biosynthesis is repressed by these steroids. The data also suggest that synthesis of lutropin alpha and beta subunits is coordinately expressed in certain physiological situations.