Mapping of DH sites between the IL-3 and GM-CSF genes. (A) Mapping of GM-CSF enhancer and promoter DH sites in an EcoRI fragment in DNase I-digested nuclei isolated from either unstimulated cells (−) or cells stimulated for 4–6 hr with 20 ng/ml PMA and 2 μM A23187 (+). On the right, the letters indicate DH sites at the GM-CSF promoter (P), GM-CSF enhancer (E), and a site at −4.4 kb present predominantly in myeloid cells (M). (A and B) The first three lanes from the left hand side are a HindIII digest of λ DNA (molecular weight marker), total non-DNaseI-digested Jurkat DNA, and a partial HindIII digest of Jurkat DNA, respectively. The lanes labeled T cells are human peripheral blood T cells. (B) Mapping of DH sites in the BamHI fragment downstream of the IL-3 gene as in A. * marks an inducible DH site present in some cell lines. (C) Map of identified DH sites together with the probes used to identify them. The transgene constructs used to make transgenic mice also are shown. (D) Mapping of DH sites in Jurkat and K562 cells as in A but at higher resolution.