Diagrams and expression of constructs containing the μLCR and β-globin gene with promoter truncations. (A) Is for constructs containing the β-globin gene extended to include the 3′ enhancer sequence, while (B) is for constructs containing the β-globin gene without the 3′ enhancer. In the diagrams to the left, the μLCR is indicated by the thick hatched bar, while the β-globin gene is indicated by the thin open bar. Exons are indicated by the open boxes, the site of transcription initiation (cap site) by the arrow, and the positions of the individual promoter truncations are relative to the cap site. To the right of each panel is indicated the number of transfected MEL585 pools included in the analysis along with the mean and range of expression for each construct.