Abstract
The gene encoding the hypothalamic peptide thyrotropin releasing hormone (TRH) was isolated from two rat genomic bacteriophage libraries. Southern blot analysis indicates that the gene is present as a single copy in the rat genome. The transcriptional unit is 2.6 kilobases in size and contains three exons interrupted by two introns of approximately 750 and 450 base pairs. Exon 1 encodes the 5'-untranslated region of the mRNA, exon 2 encodes the signal sequence and the majority of the amino-terminal peptide, and exon 3 encodes the remainder of the amino-terminal peptide, five copies of the TRH sequence, the carboxyl-terminal peptide, and the 3'-untranslated region of the mRNA. The general structure of the TRH gene resembles that of three other polypeptide hormone genes, preproopiomelanocortin, preproenkephalin A, and preproenkephalin B. Further sequence analysis revealed that characteristic promoter elements are present in the 5'-flanking region of the TRH gene. In addition, sequence homologies with the glucocorticoid receptor binding site, the GC box hexanucleotide, and a portion of the flanking region of the thyroid stimulating hormone beta-subunit gene were also identified. These upstream sequences may be important for the regulation of TRH gene expression.
Highlights
The gene encoding the hypothalamic peptide thyrotropin releasing hormone (TRH)was isolated from two rat genomic bacteriophage libraries
Further sequence analysis revealed that character- precursor expressed in Xenopus skin, which contains at least istic promoter elements are present in the 5”flanking four copies of the TRH sequence [14]
Isolation of the Rat TRH Gene-During the initial screening of 200,000 bacteriophage plaques from the XCharon4A library, eight positive recombinant bacteriophage were selected
Summary
From the Divisions of Molecular Medicine and Endocrinology,New England Medical Center Hospitals, Boston, Massachusetts 02111. Our laboratory isolated a nearly full length TRH cDNA from a rat hypothalamic bacteriophage Xgtll expression library [13] This cDNA encoded a protein of molecular of three other polypeptide hormone genes, preproopi- weight 29,247 containing five copies of the sequence, Glnomelanocortin, preproenkephalin A, and preproenke- His-Pro-Gly, flanked by paired basic amino acid cleavage phalin B. Structural and nucleotide sequence analyses indicate that the isolated genomic fragments contain the entire transcriptional unit of the TRH gene in addition to several kilobases of 5’- and 3‘-. The 5'-flanking region of the TRH gene contains several DNA elements known to be important in the regulation of other cellular genes
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