Identification of DNase I hypersensitive sites at −23 −28 kb in the upstream Kit region. Nuclei were prepared from +/+,W^sh/W^sh andW⁵⁷/W⁵⁷BMMC and from Kit expressing HCD57 and melan-a cells and liver, and digested with DnaseI. DNA was restricted with the restriction enzymes Sac1 and BamH1 (as indicated), fractionated by electrophoresis, and analyzed by blot hybridization. A Kpnl-Alul probe detected one hypersensitive site in the Sac1 fragment located at −23 −28 kb in +/+ BMMC, near the 3′ W⁵⁷ deletion endpoint. No hypersensitive site was detected in DNA from W⁵⁷and W^sh BMMC and from liver nuclei. The same Kpnl-Alul probe detected two hypersensitive sites in theBamHl fragment located at −21 −25 in +/+ that were absent in W⁵⁷ BMMC. Whereas in DNA from melan-a cells HS4-6 were absent, a new hypersensitive site HSM1 was detected. Horizontal arrows identify sub-bands generated by hypersensitive sites. Size markers are indicated. A schematic representation of the hypersensitive sites in the distal Kit promoter region around −21 to −28 kb is shown below.