MOLECULAR CLONING AND SEQUENCE ANALYSIS OF THE TWO GONADOTROPIN B-SUBUNIT cDNAs OF BLUNT SNOUT BREAM(MEGALOBRAMA AMBLYCEPHALA)

The cDNAs encoding B-subunits of gonadotropin hormone I (GtH IB) and gonadotropin hormone ?(GtH IIB) have been cloned from pituitary of blunt snout bream (Megalobrama amblycephala) using reverse transcript ion- polymerase chain reaction (RT-PCR) and rapid amplification of cDNA end (RACE) methods.Then, amino acid sequence and phylogenetic relations were analysed.The GtH IBsubunit cDNA is 567 base pair(bp) that comprises of a 5.-UTR of 26bp, a 3.-UTR of 148bp and an open reading frame (ORF) of 393bp which encodes a 130 amino acid protein with a signal peptide of 22 amino acids and a mature peptide of 108 amino acids.On the other hand, GtH IIBsubunit cDNA is 564bp that comprises of a 5.-UTR of 43bp, a 3.- UTR of 95bp and an ORF of 426bp which encodes a 141 amino acid protein with a signal pept ide of 24 amino acids and amature pept ide of 117 amino acids.The amino acid sequence identities of Megalobrama amblycephala GtH IBand GtH IIBsubunits in comparison with other 15 fishes including Mylopharyngodon piceus are 90%)31% and 95%)41%, respectively; while in comparison with 5 tetrapods including Rana Ridibunda are 38%)21% and 49%)36%, respectively.Both GtH IBand GtH IIBsubunits of Megalobrama amblycephala resemble most to those of Cyprinidae, implying their closer phylogenetic relat ionship.In addition, both Megalobrama amblycephala GtH IBand GtH IIBsubunits have 12 conserved cysteine residues and 1 N- linked glycosylation site.