Identification of separate mRNAs coding for the alpha and beta subunits of thyrotropin.

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Abstract
A 9S mRNA purified from mouse thyrotropic pituitary tumors [TtT97] by sucrose density gradient centrifugation of poly(A)-enriched mRNA, directed the synthesis of only .alpha. and .beta. subunits of thyrotropin [TSH] in the reticulocyte [rabbit] lysate translation system. Analysis of radioiodinated 9S mRNA, repurified by oligo(dT)-cellulose chromatography and sucrose gradient centrifugation, yielded 2 spp. of RNA on urea/polyacrylamide gel electrophoresis. The major RNA species containing 620 nucleotides and the minor RNA species contained 560 nucleotides. Unlabeled 9S mRNA was further purified by urea/polyacrylamide gel electrophoresis; the mRNA were separately eluted from slices of the gel containing material migrating with an apparent length of 620 and 560 nucleotides. Translation of these mRNA in the reticulocyte lysate showed that the longer mRNA coded for the .alpha. subunit and the shorter mRNA coded for the .beta. subunit of mouse TSH. Because more .alpha. than .beta. subunit of TSH was consistently synthesized, unbalanced amounts of TSH subunits appear to be synthesized by translation of unbalanced amounts of individual mRNA. The synthesis of TSH is apparently directed by 2 separate mRNA molecules, each coding for a different subunit of the hormone.