Molecular cloning and sequencing of salmon gonadotropin β subunit

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Abstract
Gonadotropin (GTH) was purified from the pituitaries of the Pacific chinook salmon using a combination of stepwise ethanol precipitation and concanavalin‐A affinity chromatography. The α and β subunits were dissociated and fractionated by C‐18 reverse‐phase high‐performance liquid chromatography with a 0.1% trifluoroacetic acid/acetonitrile gradient. An enriched cDNA library was screened for the β‐GTH gene(s) using two synthetic oligonucleotides based on partial protein data. A positive, full‐size clone (E3) was identified and sequenced. It contains 657 base pairs and codes for a 142‐amino‐acid precursor protein. The mature salmon β‐GTH (119 amino acids) is structurally homologous to human luteinizing hormone and chorionic gonadotropin. The effect of testosterone implantation on pituitary GTH and β‐GTH mRNA was examined with radioimmunoassay and Northern blot analysis. There was a corresponding increase in both the pituitary GTH and mRNA levels.