Cloning of cDNA encoding the pre-beta subunit of mouse thyrotropin.

Abstract
Double-stranded c[complementary]DNA was synthesized from sucrose gradient-purified poly(A)+ mRNA from a mouse thyrotropic tumor, inserted into the Pst I site of plasmid pBR322 by using poly(dC).cntdot.poly(dG) homopolymeric extensions, and cloned in Escherichia coli RRI. Plasmids containing cDNA sequences coding for the .beta. subunit of thyrotropin (TSH) were identified by cell-free translation of hybrid-selected mRNA and immunoprecipitation with specific antibody to TSH .beta. subunit. Determination of the nucleotide sequence of 1 cDNA, 595 base pairs in length, allowed deduction of the entire amino acid sequence of the mouse TSH .beta. subunit. The pre-.beta. subunit contains a 20-amino acid mature TSH .beta. subunit. There is 85-90% homology in amino acid sequence between mouse TSH .beta. subunit and subunits from man, pig, and cow; however, the mouse subunit contains an additional 5 or 6 amino acids at its carboxyl terminus compared to the bovine or human and pig subunits, respectively. TSH .beta.-subunit mRNA from mouse thyrotropic tumor was estimated to be 750 nucleotides in length by hybridization with labeled TSH .beta.-subunit cDNA.