A DNase I HS site maps near exon 9 in the MLLBCR. Restriction map of the MLL BCR and adjacent regions are represented. Exons, SARs, and restriction enzymes are the same as in Fig 1. The restriction map is not drawn to scale centromeric or telomeric to the double thick black diagonal lines (//). The large black arrow above the map represents the strong DNase I cleavage site near exon 9. Probes are represented as grey hatched boxes above the map, and the 7 small black arrows above the map represent potential topo II in vivo cleavage sites identified by computer analysis.30 Thin black lines below the map identify germline fragments that hybridize with the probes above. Thick lines below the map represent the new DNase I fragments that are only observed after DNase I digestion. Note that only BamHI andBgl II germline (thin lines) and DNase I (thick lines) fragments are represented below the restriction digest map to show examples of our results. The table below the map represents a summary of the DNA restriction digests, the gene probes, and DNase I HS results correlated with the MLL map. The two top rows for each set of results correspond to the probes hybridized (in bold) to DNA isolated from DNase I–treated nuclei and digested with particular enzymes (second row, or otherwise indicated). Restriction enzymes:BamHI (B), Bgl II (Bg), EcoRI (E), NcoI, and Pst I. Results are indicated as + for the presence of DNase I HS, − for negative for DNase I HS, and nd for not determined.