BOVINE THYROTROPIN RECEPTOR CDNA IS CHARACTERIZED BY FULL-LENGTH AND TRUNCATED TRANSCRIPTS

The complete coding sequence for the bovine thyrotropin (TSH) receptor was derived using a modified PCR cloning strategy. The bovine thyrotr opin receptor conforms to the pattern of receptor interacting with mem brane-bound G-protein already established in other species for TSH and gonadotropins receptors. The cDNA for the bovine TSH receptor consist s of an open reading frame 2289 nucleotides in length, corresponding t o a protein of 763 amino acids (estimated molecular mass of 86.4 kDa) which includes a 20 amino acid putative leading signal peptide. The re ceptor consists of a lame NH2-terminal extracellular membrane domain o f 417 amino acids with 5 potential N-linked glycosylation sites, a tra nsmembrane domain (265 amino acids) consisting of 7 putative membrane alpha-helix spanning segments, and an intracytoplasmic COOH-terminal d omain (82 amino acids). The bovine TSH receptor is one amino acid less than the corresponding sequence in dog, human, rat and mouse. Cystein e residues (n=22) were conserved when compared with other TSH receptor s. Three potential phosphorylation sites were found in the transmembra ne domain and the COOH-terminal domain. As with other members of this receptor family, alternative splicing was observed. A transcribed but truncated TSH receptor of 1769 nucleotides was demonstrated, lacking h alf of the V segment of the transmembrane domain up to the COOH-termin al domain of the full length TSH receptor. Additionally, alternative t ranscriptional start sites were observed. Northern blot analysis using a probe (1170 bp) spanning part of the extracellular domain up to the first loop of the transmembrane domain showed specific expression in the bovine thyroid gland with major transcripts of 9.3 and 4.3 kb, and a minor transcript of 3.8 kb being detected.