Examples of previously unidentified DNase HSs in the mGata1 locus. (A) The mGata1 locus is depicted as in Figure 1A. The positions of constitutive (black arrows) and hematopoietic (gray arrows) DNase I HSs are marked. Below, a gray bar indicates the region of chromatin, which was systematically surveyed throughout for DNase I HSs. (B-G) Maps of the relevant portions of the genomic mGata1 locus, together with examples of DNase I HSs, are shown. Gray boxes illustrate position of the probes used in the Southern blot analysis. A box and an arrow mark the position of the DNase I HS. Genes are depicted as open boxes; exons, as gray blocks. Restriction enzymes used include RI, EcoRI; X, XbaI; HIII, HindIII; and B, BamHI. Coordinates in kilobases are shown below each map with respect to GATA1 IE promoter transcriptional start site. Below, autoradiographs demonstrate DNase I HS. Nuclei from different primary cells and cell lines, as indicated in each panel, were digested with increasing concentrations of DNase I, as illustrated by triangles. Abbreviations for cells used are as follows: MEL, erythroleukemia cell line; L8057, megakaryocytic cell line; I^o eos, primary eosinophils; and 3T3, fibroblast cell line. No exogenous DNase I was added to the first lane. Extracted DNA was then digested with different restriction enzymes as indicated in each panel. On the right of the autoradiograph are the positions of the limit digest (LD), DNase I hypersensitive sites, and DNA molecular weight markers in kilobases.