Diagram and expression of constructs designed to test the enhancing activity of HS-40 and novel cassettes for^Aγ-globin. (A) Is for constructs containing the^Aγ-globin gene (thin filled bar) with the −382 promoter and various arrangements of the HS-40 enhancer, (B) is for constructs containing the β-globin gene with the −267 promoter (thin open bar) and various arrangements of the HS-40 enhancer, and (C) is for constructs containing hybrid expression cassettes with the β-globin promoter, various versions of the ^Aγ-globin gene, and a single copy of the HS-40 enhancer in the same orientation. Exons are indicated by the boxes, the sites of transcription initiation (cap sites) by the arrows, and the segments of the β-globin promoter and^Aγ-globin intron 2, which were deleted, are indicated by a thin line. The HS-40 enhancer is indicated by the thick bars with graded fill, and the orientation is shown underneath by an arrow. To the right of each panel is indicated the number of transfected MEL585 pools included in the analysis, along with the mean, standard deviation, and range of expression for each construct as described in the legend to Fig 1.