title: Molecular cloning of cDNAs encoding two gonadotrophin beta subunits (GTH-I beta and -II beta) from the masu salmon, Oncorhynchus masou: rapid divergence of the GTH-I beta gene.
abstract: Two types of cDNA (GTH-I beta and -II beta) encoding the beta subunit of masu salmon (Oncorhynchus masou) gonadotrophin were cloned using the reverse transcription-polymerase chain reaction for pituitary mRNAs. The nucleotide sequence of GTH-I beta cDNA was 469 bp long, encoding 137 amino acids, and GTH-II beta cDNA was 476 bp long, encoding 142 amino acids. These two masu salmon beta subunit types showed low homologies of 52% (nucleotide sequence) and 33% (amino acid sequence). The evolutionary interval between masu and chum salmon was estimated to be 5.65 and 1.43 million years by comparing GTH-I beta and GTH-II beta respectively. These time values are markedly inconsistent with the evolutionary time (3.0 million years) estimated from fossil records and an isozyme study. Southern blot analyses showed that the I beta gene restriction fragment lengths differed among five teleosts, whereas, with one exception, the II beta gene showed well conserved patterns. Therefore, the GTH-I beta gene may have diverged at a faster rate than the GTH-II beta gene.
authors.affiliation: Hormone Assay Center, Gunma University, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Kato
authors.forename: K
authors.initials: K
authors.lastname: Gen
authors.forename: O
authors.initials: O
authors.lastname: Maruyama
authors.forename: K
authors.initials: K
authors.lastname: Tomizawa
authors.forename: T
authors.initials: T
authors.lastname: Kato
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics*; D005399:Fishes / Q000235:genetics; D006065:Gonadotropins, Pituitary / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D017685:Oncorhynchus keta / Q000235:genetics; D011487:Protein Conformation; D012474:Salmon / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity
chemical_list: D018076:DNA, Complementary; D006065:Gonadotropins, Pituitary; C057763:gonadotropin- pituitary, beta-subunit I, salmon