Fig. 6. Elimination of spliced Tsix RNA does not affect the establishment of closed chromatin structure. Chromatin structure in the 5 ' region of Xist was analyzed by the DNaseI hypersensitive site assay. The diagrams show the structure of the Xist/Tsix locus, and the positions of DNaseI hypersensitive sites identified on the respective mutated X chromosome as well as those of HindIII sites used for the digestion of purified DNA. The position of the probe (Af0.4) used for Southern hybridization is also indicated. Ectopic DNaseI hypersensitive sites detected on X^dc are not found in E13.5 embryos carrying Tsix^SA. White arrowheads indicate the fragment derived from HS3 on the mutated X; black arrowheads indicate those from HS1 and HS5 on the mutated X. H, HindIII.