Analysis of endonuclease sensitivity in the −^ZF chromosome.

DNA from nuclei of (A) EBV lymphocytes, (B) an interspecific MEL hybrid containing the α−^ZF chromosome (ZF2), and (C) the erythroid cell line K562. The DNA was incubated with increasing amounts of Hinf I (“Materials and methods”) and analyzed with probes around gene no. 6 (RA0.6, approximate coordinate 67 000), which encodes the ubiquitously expressed MPG gene, the α-globin regulatory element HS –40 (approximate coordinate 103 000), and the α-globin gene. Whereas the site associated with HS –40 is clearly present in ZF2, the sites are missing from the silenced α-globin promoter.