Map of transgene constructs designed to determine the importance of specific human β-globin gene sequences in LCR activity conferred by the 5′HS3 element.

The sequences used in each construct are outlined in “Materials and methods.” The β-globin gene is indicated as a thick line with exons as black boxes. β-globin gene regulatory elements are indicated by black arrows and include the 815-bp β-globin promoter (Prom), the AT-rich region (AT) that coincides with a known MAR and intragenic enhancer (Enh) located in intron 2, and the 260-bp 3′ enhancer (Enh) located downstream of the gene. Aγ-globin gene sequences are represented as thin lines, and unfilled boxes (exons) or arrows (regulatory elements). Southern probe fragments correspond toXhoI-XhoI fragment of 5′HS3 in BGT9 (A),BamHI-EcoRI fragment of β-globin intron 2 in BGT9 (B), and EcoRI-EcoRI fragment of Aγ-globin 3′ sequences in BGT26 (C).