A unique HS site appears 5′ of the proximal promoter in PHZ-treated −4.0 TG mouse spleen nuclei. (A) Location of the probe used for the detection of DNase I HS sites is indicated (dark hatched box) in the context of both the human ferrochelatase genomic locus (top) and the luciferase reporter transgene (bottom). The black box represents exon 1, open boxes represent SV40 sequences, and the light hatched box represents the luciferase reporter gene from p19 Luc (B, BamHI; P, PstI; and Xb, Xba I). (B) Nuclei were isolated from both normal and PHZ-treated spleens from −4.0 TG mice. After DNase I digestion of intact nuclei, DNA was isolated, digested to completion withBamHI, and the resulting fragments were identified by using the indicated probe in Southern blot analysis. The resulting fragments and their sizes are indicated. (C) Location of putativecis-elements as deduced from the analysis of the primary structure of the hypersensitive region and surrounding sequences (top). The open box (at −2.05 kb to −2.2 kb) indicates the AT-rich region. The location of this HS region and surrounding sequences within the transgene is indicated (bottom).