Effect of deletion of HS-E1 from the endogenous β-globin locus on gene expression and RNA Pol II association. (A) Homologous recombination strategy for the deletion of HS-E1. (B) β-globin mRNA expression analysis for E8.5 and E12.5 peripheral blood, and for E14.5 fetal liver, derived from wild-type embryos and embryos homozygous for the deletion of HS-E1. All values are derived from averages of at least 6 individual embryos. (C) RNA Pol II ChIP analysis in E12.5 peripheral blood. Enrichment for RNA polymerase II association with the indicated sequences is calculated using inactive control loci as background controls (ie, 1.0).