| A cDNA fragment of 1.8kb designated as RSD-2(GenBank Accession Number: M31322) was previously isolated from a rat testis cDNA expression library with a monoclonal antibody of sperm membrane protein YWK-II antigen. By screening human testis cDNA libraries with RSD-2 and using rapid amplification of cDNA ends (RACE), human cDNA sequence of 3135bp corresponding to YWK-II antigen designated as HSD-2 was obtained with an ORF of 590 codons. Upon homology analysis, YWK-II antigen has wide-ranging homology to Alzeimer' s amyloid precursor protein with typical characteristics of single-transmembrane proteins, contains threedomains-extracellular, hydrophobic transmembrane andcytoplasmic domains, and has very high homology to APPH/APLP2, which is a member of APP protein super-family, isolated from human placenta expression library. It showed that YWK-II and APP belong to the same protein super-family with similar functions with their homologous domains.The gene of YWK-II antigen was assigned to 11q2.4-2.5 by means of fluorescence in situ hybridization (FISH), while APP gene maps to the human chromosome 21.YWK-II antigen was previously immunolocalized to the equatorial sector of human sperm head. This site on the sperm head participates in the fusion of sperm to egg membrane during fertilization. Presently, in order to learn the potential functions of YWK-II antigen, three cDNA fragments with various characteristics were cloned into expression vector and expressed in E. coli and eukaryotic cells and the function for the...
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