Figure 2

DNase I hypersensitivity mapping upstream of XIST. Below the schematic of the XIST region (see legend in Figure 1) are Southern blots of DNA from ES-10, an Xa hybrid, and an Xi hybrid. Small rectangular boxes are probes for Southern blotting of overlapping restriction fragments (from left to right: Pst I (13.1 kb); Bsm I (10.3 kb); Nde I (7.2 kb); Sap I (6.7 kb); Spe I (6.3 kb); Sca I (3.8 kb)). All experiments were carried out at least twice. One HS site, highlighted by the open arrow, was detected just upstream of the transcriptional start site, within the Spe I fragment, at somewhat variable positions in the three cell lines. Another HS site was found within the Bsm I fragment approximately 65 kb upstream of the XIST transcription start in both Xa and Xi hybrids (grey arrow). No other DNase I hypersensitive sites were observed.