The Sfpi1/PU.1 locus. (A) A 35-kb segment of mouse chromosome 2 is represented with the DNA encoding Sfpi1/PU.1 (thin black rectangles), the transcription start site (open arrow), and the −14-kb upstream regulatory element (URE) as a gray box. Predicted erythroid cis-regulatory modules (CRMs)⁶³  and amplicons used in chromatin immunoprecipitation (ChIP) assays are shown as rectangles above and below the line, respectively, with the positions of the amplicons relative to the transcription start given in kilobases. The positions of GATA consensus binding motifs (WGATAR), both conserved in mammals and present only in rodents, are indicated as vertical lines. The track labeled “regulatory potential” plots sequence similarity to alignment patterns in known regulatory regions.⁶²  Rows labeled “conservation” show interspecies alignments with the mouse genome; darker lines indicate greater sequence similarity. (B) The sequence of the PU.1/Sfpi1 promoter region. A PU.1 binding site (AGGAA) is located just downstream of the transcription start site, which is indicated by the arrow. A GATA-1 binding site (CTATCT) is located 27-bp upstream of the PU.1 binding site.