Exons 1, 2, and 3 as well as 5 kb of the proximal promoter were deleted via cre mediated recombination of single loxP sites in the 5' untranslated region and intron 3. Though complete transcriptional ablation was previously reported by Csankocszki et al., 1999 (J:75502), Turner et al., 2002 (J:80117) reported an endogenous testis-specific transcript that utilizes an upstream promoter in wild-type mice and therefore is putatively present in mutant mice. The deleted region encoded a domain essential for X chromosome inactivation.