A 2.5 kb sequence was deleted between 5.5 and 8 kb upstream of Xist, including Rps12-ps1 and spanning a site thought to include an upstream promoter for Xist. A floxed PGK-neo was also inserted. RT-PCR showed presence of antisense transcription upstream of Xist in mutants where none is present in wild-type. (J:85305)