Schematic representation of the human β-globin locus and sequences upstream of the LCR 5'HS5 region A) The human β-globin locus YAC (β-YAC). The ~187 kb EcoRI genomic DNA fragment containing the human β-globin locus is shown as a line above the YAC map. The β-like globin genes and YAC arms are shown as black rectangles. The LCR HSs are denoted with arrows. YAC arms contain a centromere (CEN), an autonomous replication sequence (ARS1), selectable markers for tryptophan and lysine prototrophy (TRP1 and LYS2, respectively), and an MMTneo cassette for selection in mammalian cell culture. B) Wild-type sequence with pertinent restriction enzyme sites labeled above and below the line. The 683 bp ScaI-SfiI probe used for Southern blot hybridization is indicated by the grey bar. C) A 55 bp loxP-AscI site was inserted into the SfiI site at nucleotide 31,061 by YIP-mediated homologous recombination. The numbering is based on GenBank file AF137396.