The DNaseI hypersensitive sites (HSS) in TF-1, independent of downregulation or upregulation of the c-kit receptor, are identical. (A) Mapping of HSS (1-4) (arrowheads) in different TF-1 cell lines. All major and minor degradation bands of the 4.2-kbEcoRI fragment are indicated and numbered according to the map of (B). HSS1 directly maps within the c-kit promoter region. HSS2, HSS3, and HSS4 are located in the 5′ region of the first intron. DNaseI-treated genomic DNA (10 μg) was digested with EcoRI and probed with probe (a). DNaseI concentrations were as follows: lane 1, no DNaseI; lane 2, 0.8 μg/mL; lane 3, 1.2 μg/mL; lane 4, 1.8 μg/mL; lane 5, 2.7 μg/mL; lane 6, 4.0 μg/mL. (B) The hypersensitive sites of the c-kit promoter region of TF-1 cells (TF-1; TF-1S #MB3, #MB6, #MB8; and TF-1S #MBs removed from stroma for 1 day). HSS4 is a minor site and was not always found. Exon 1 is boxed, and the coding region is indicated by shading. Probes used for mapping HSS (a and b) are indicated.