Open AccessmRNA-directed biosynthesis of α subunit of thyrotropin: Translation in cell-free and whole-cell systems
Author(s) -
Ione A. Kourides,
Bruce D. Weintraub
Publication year - 1979
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.76.1.298
Subject(s) - reticulocyte , protein subunit , biology , biochemistry , immunoprecipitation , gel electrophoresis , microbiology and biotechnology , xenopus , antiserum , translation (biology) , sodium dodecyl sulfate , messenger rna , gene , antibody , genetics
mRNA from mouse thyrotropic pituitary tumors was translated in frog oocytes (a whole-cell system) and in wheat germ extract and reticulocyte lysate (cell-free systems) in the presence of [35 S]methionine. Synthesized peptides related to thyrotropin were identified in the three systems by immunoprecipitation with subunit-specific antisera developed against the α subunit of ovine lutropin (luteinizing hormone) and the β subunit of bovine thyrotropin. In wheat germ extract and reticulocyte lysate, a single immunoprecipitable form of the α subunit of thyrotropin was synthesized with an apparent molecular weight of 14,000 by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. In the frog oocyte, three forms of immunoprecipitable α subunit of thyrotropin were synthesized with apparent molecular weights of 20,000, 14,000, and 10,000. The 20,000 form is similar to unlabeled rat pituitary standard α subunit and35 S-labeled mouse tumor α subunit in cell cultures (20,000-21,000); thus, it may represent a precursor-cleaved and glycosylated form. The 14,000 form synthesized in all three systems probably represents the pre-α subunit of thyrotropin; the 10,000 form, synthesized only in the frog oocyte, could be a proteolytically cleaved but unglycosylated form. Because only the α subunit of thyrotropin was identified and no larger molecular weight immunoprecipitable form of either subunit was detected in any of the translation systems, α and β subunits of thyrotropin appear to be translated from separate mRNAs.