The correlation of anti-sperm antibodies with cases of unexplained infertility implicates a role for these antibodies in blocking fertilization. Improved diagnosis and treatment of immunologic infertility, as well as identification of proteins for targeted contraception, are dependent on the identification and characterization of relevant sperm antigens. The protein encoded by this gene is recognized by sperm agglutinating antibodies from an infertile woman. This protein is localized in germ cells of the testis at all stages of spermatogenesis and is localized to the acrosomal region of mature spermatozoa. This protein interacts with ACT (activator of CREM in testis) and may play a role in CREM (cAMP response element modulator)-ACT-mediated gene transcription during spermatogenesis. This protein may also play a role in spermatogenesis by regulating microtubule formation and cell division. Alternatively spliced variants that encode different protein isoforms have been described but the full-length sequences of