Molecular cloning and expression of salmon pituitary hormones

A cDNA library was prepared from chinook salmon pituitaries. Growth hormone (GH), prolactin (PRL) and the β subunit of gonadotropin (GTH) genes were screened using synthetic oligonucleotides as probes. Full size cDNA clones coding for these polypeptide hormones were isolated and characterized. The cDNA sequences for PRL and βGTH have been reported earlier from our laboratories. The cDNA clone for GH contains 1148 bp and codes for a preGH of 210 amino acids. The chinook salmon GH, reported in the present investigation, differs from chum salmon GH in only 1 amino acid, and from coho salmon GH in 5 amino acids. Plasmids containing modified nucleotide sequences coding for GH, PRL and βGTH were constructed individually into an expression vector using the heat-inducible λ pL promotor. Mature PRL, GH and unglycosylated βGTH were expressed in the bacteria at elevated temperature.