FIG. 2.

DNA sequence of the human HPRT promoter region. Boxes indicate positions of transcription factor binding sites. Circles indicate positions of dimethyl sulfate (DMS) in vivo footprints, closed circles represent DMS protections, and open circles represent sites of enhanced DMS reactivity. The thin horizontal line indicates the region of multiple transcription initiation sites, with bent arrows indicating the major sites of transcription initiation. Ovals indicate positions of methylated CpGs critical for transcriptional repression. +1 indicates the translation initiation site, with exon 1 shown in boldface. The large gray box indicates the region deleted by homologous recombination.