FIG. 4.

Physical map of the human HPRT gene. The thick horizontal line represents the HPRT gene. Open horizontal boxes represent exons, and “ATG” indicates the translation initiation site. The bent arrow represents the major transcription initiation sites, and a putative initiator element is shaded. The gray box indicates the position of probe “HPRT A.” The bracket above the line indicates the position of the 5′ flanking DNase I-hypersensitive site. The positions of CpG-dinucleotides within the gene are shown as vertical lines below the gene map. Numbers indicate the position of CpGs relative to the translation initiation site. The horizontal bracket below the line indicates the region deleted in Δ2B and Δ3B cells.