DNAse I hypersensitive site mapping of the vavgenomic locus in hematopoietic cells and fibroblasts. (A) Diagrams of the probes, digests, and observed fragment sizes (in kilobases) that delineated the five major HS sites in (B) through (D). Exons are shown as solid boxes. Nuclei from FDC-P1 cells and NIH3T3 fibroblasts (B and C) or C88 murine erythroleukemia (MEL) cells (D) were digested with increasing amounts of DNase I followed by Southern analysis of extracted DNA, using the indicated restriction enzyme/probe combinations. The sizes of the germline fragments (G) and the DNase I cleavage products at each HS site are indicated in kilobases. The additional germline band of approximately 4.5 kb in NIH3T3 cells (B) reflects a polymorphic Bgl II site approximately 1 kb 5′ of the first vav exon. In (C), the 4.7-kb band (G 4.7) reflects detection of the 4.7-kb germline Xba fragment (see [A]) by exon I sequences in cDNA probe b. On prolonged exposure, bands corresponding to HS2,1 and 4 were also seen. In (E), fine mapping of the proximal vav promoter demonstrates that HS1 comprises two sites approximately 400 bp apart. The positions of the stronger HS1a and weaker HS1b sites and probes c and d are indicated on the diagram. Abbreviations: X, Xba I; S, Sac I; Hp,Hpa I; Bg, Bgl II.