Map of the human β-globin LCR transgene constructs designed to determine the importance of 5′HS1, distal β-globin promoter, and 3′ sequences in directing full transgene expression levels in single-copy transgenic mice. The activity of the microlocus and BGT14 constructs has been previously described,11,21and the specific sequences used in each construct are outlined in Materials and Methods. The black boxes in each HS correspond to the known core elements, and the black boxes in the β-globin gene correspond to the three exons. The length of each promoter (Pr) is given below the line, and the enhancers (En) located in the second intron and 3′ of the gene are indicated. A, Acc1; B,BamH1; E, EcoR1; N, Nco1.