A cDNA clone, pc17bHSD, was obtained from the chicken ovarian cDNA library by its partial homology to the cDNA sequence of the rat 17β-hydroxysteroid dehydrogenase (17β-HSD). The cDNA insert of pc17bHSD is 979 bp long and contains an open reading frame (ORF) of 906 bp. The deduced amino acid sequence of the ORF shows 48 and 50% overall identity with those of the rat and the human type-1 17β-HSD, respectively. Five sequence regions common to the short-chain alcohol dehydrogenase superfamily are well conserved, including the YxxxK sequence motif at the active site. Northern blot hybridization detected a transcript of about 1 kb only in ovaries of both sexually immature and mature female chickens. The 17β-HSD activity, which was highly specific to the interconversion between estrone and estradiol-17β, was detected in the cytoplasmic fraction of human 293 cells transfected transiently with an expression vector carrying the c17bHSD cDNA sequence, pcDNAI/c17bHSD. From these results, it is concluded that the pc17bHSD is the cDNA clone for the ovary-specific molecular species of 17β-HSD in chickens.
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