RNA polymerase II association with α- and β-globin gene sequences in primitive erythroid cells. Enrichments are shown in bar graph format relative to multiple control sequences elsewhere in the β-globin locus, of crosslinked chromatin samples immunoprecipitated using antiserum against RNA polymerase II, as determined by quantitative real-time PCR. ▪ represent enrichments at the indicated β-globin gene promoters, while □ represent enrichments at sequences located within the third exon or immediately downstream of the stop codon for each gene, approximately 1 kb 3′ of the promoters. The border between shaded and unshaded regions represents relative enrichment of 1.0-fold (ie, no enrichment [arrowhead]). The data shown represent averages of at least 3 PCRs for each sequence examined, derived from 2 (E10.5) or 3 (E12.5) separate immunoprecipitations. Error bars represent SEM.