Rainbow Trout Growth Hormone: Molecular Cloning of cDNA and Expression in Escherichia coli

We have isolated several recombinant clones carrying the complementary DNA (cDNA) sequence of the rainbow trout (rt) Salmo gairdneri growth hormone (GH) mRNA by immunoblot screening using an antiserum to chum salmon (Oncorhyncus keta) GH. The nucleotide sequence of one of the rtGH cDNA clones (pAF51) was determined. The rt cDNA sequence in pAF51 encodes a hybrid polypeptide of 199 amino acid residues containing 9 amino acid residues of the bacterial beta-galactosidase, one residue from the codon at the junction of the beta-galactosidase gene, and the rtGH cDNA sequence, an additional residue from the presumptive signal peptide of the pre-rtGH and the entire sequence of the mature rtGH (188 amino acid residues). Pairwise matrix comparisons of the hydropathy profiles of bovine, human, rat, and rainbow trout GH polypeptides indicate that regions of similarity exist between the rtGH and mammalian GH. In particular, there are two major regions of similarity found near the amino-terminal region and at the carboxy-terminal region. These regions correspond to hydrophilic domains of the GH molecules. The possible significance of these domains is discussed.