We have previously reported a mouseRnf33⁄Trim60gene that is temporally expressed in the pre-implantation embryo. TheRnf33structural gene is com-posed of a short noncoding exon 1 and an intronless coding exon 2. In the present work,Rnf33was shown to be expressed in the mouse testis and in the testicular cell lines TM3 and TM4.