Human testis specific protein: a new member of aldo-keto reductase superfamily.

Human testis specific protein, HTSP, was identified initially by the search of the Expressed Sequence Tag database, followed by the screening of human testis cDNA library. Among various organs examined, the HTSP transcripts were detected only in the testis, not in other reproductive organs such as vas deferens and prostate. No cross-hybridizing signal was detected in the testis of mouse or rat, indicating that this gene is specifically expressed in the human testis. We isolated four isoforms, HTSP1, 2, 3 and 4. Screening of the high throughput genomic sequence database indicated the localization of the HTSP gene in chromosome 10. Thus, HTSP isoforms were generated by alternative splicing of a single gene. HTSP4, the longest gene product, was composed of 307 amino acids and shared 56% identity to mouse vas deferens protein as well as human aldose reductase in amino acid levels. Bacterially expressed recombinant HTSP protein showed small but significant activity towards 9,10-phenanthrenequinone among the putative substrates so far tested. Accordingly, HTSP is a new member of the aldo-keto reductase superfamily with as yet unidentified function.