Rat P45017αfrom Testis: Characterization of a Full-Length cDNA Encoding a Unique Steroid Hydroxylase Capable of Catalyzing Both Δ4- and Δ5-Steroid-17,20-Lyase Reactions

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Abstract
A cDNA clone encoding the complete rat 17.alpha.-hydroxylase (P45017.alpha.) from testis has been identified and sequenced. The deduced amino acid sequence is found to have 69% similarity with human P45017.alpha., 64% similarity with bovine P45017.alpha., and 47% similarity with chicken P45017.alpha.. The protein contains 507 amino acids being one amino acid shorter than the human P45017.alpha. as the result of a codon being absent at the position of amino acid 139 in the human sequence. The cDNA hybridizes to a single mRNA (.apprx. 2.0 kilobases) in rat testis RNA and Southern analysis indicates the presence of a single CYP17 gene in the rat genome. Expression of this cDNA in COS1 cells leads to production of a steroid hydroxylase which is capable of converting both 17.alpha.-hydroxypregnenolone and 17.alpha.-hydroxyprogesterone into C19 steroids, dehydroepiandrosterone, and androstenedione, respectively. This activity profile is distinct from that of either the human or bovine forms of P45017.alpha. which are unable to catalyze 17,20-lyase conversion of .DELTA.4-C21 steroids to .DELTA.4-C19 steroids at significant rates.