A CANDIDATE SPERMATOGENESIS GENE ON THE MOUSE Y-CHROMOSOME IS HOMOLOGOUS TO UBIQUITIN-ACTIVATING ENZYME-E1

THE human X-linked gene A1S9 (refs 1-3) complements a temperature-sensitive cell-cycle mutation in mouse L cells 4, and encodes the ubiquitin-activating enzyme E1 (refs 5-7). The gene has been reported to escape X-chromosome inactivation 8, but there is some conflicting evidence 9. We have isolated part of the mouse A1s9 gene, mapped it to the proximal portion of the X chromosome and shown that it undergoes normal X-inactivation. We also detected two copies of the gene on the short arm of the mouse Y chromosome (A1s9Y-1 and A1s9Y-2). The functional A1s9Y gene (Als9Y-1) is expressed in testis and is lost in the deletion mutant Sxr(b) (ref. 10). Therefore A1s9Y-1 is a candidate for the spermatogenesis gene, Spy, which maps to this region. A1s9X is similar to the Zfx gene in undergoing X-inactivation 11,12, yet having homologous sequences on the short arm of the Y chromosome 13,14, which are expressed in the testis. These Y-linked genes may form part of a coregulated group of genes which function during spermatogenesis.