14. Bulger M, Schubeler D, Bender MA, Hamilton J, Farrell CM, et al. (2003) A complex chromatin landscape revealed by patterns of nuclease sensitivity and histone modification within the mouse beta-globin locus. Mol Cell Biol 23: 5234–5244. 15. Imam AM, Patrinos GP, de Krom M, Bottardi S, Janssens RJ, et al. (2000) Modification of human beta-globin locus PAC clones by homologous recombination in Escherichia coli. Nucleic Acids Res 28: E65. 16. Strouboulis J, Dillon N, Grosveld F (1992) Developmental regulation of a complete 70-kb human beta-globin locus in transgenic mice. Genes Dev 6: 1857–1864. 17. Dekker J, Rippe K, Dekker M, Kleckner N (2002) Capturing chromosome conformation. Science 295: 1306–1311. 18. Wijgerde M, Grosveld F, Fraser P (1995) Transcription complex stability and chromatin dynamics in vivo. Nature 377: 209–213. 19. Bulger M, van Doorninck JH, Saitoh N, Telling A, Farrell C, et al. (1999) Conservation of sequence and structure flanking the mouse and human beta- globin loci: the beta-globin genes are embedded within an array of odorant receptor genes. Proc Natl Acad Sci U S A 96: 5129–5134. 20. Grosveld F, van Assendelft GB, Greaves DR, Kollias G (1987) Position- independent, high-level expression of the human beta-globin gene in transgenic mice. Cell 51: 975–985. 21. Gribnau J, Diderich K, Pruzina S, Calzolari R, Fraser P (2000) Intergenic transcription and developmental remodeling of chromatin subdomains in the human beta-globin locus. Mol Cell 5: 377–386. 22. Gribnau J, de Boer E, Trimborn T, Wijgerde M, Milot E, et al. (1998) Chromatin interaction mechanism of transcriptional control in vivo. EMBO J 17: 6020–6027. 23. Patrinos GP, de Krom M, de Boer E, Langeveld A, Imam AM, et al. (2004) Multiple interactions between regulatory regions are required to stabilize an active chromatin hub. Genes Dev 18: 1495–1509. 24. Tuan DY, Solomon WB, London IM, Lee DP (1989) An erythroid-specific, developmental-stage-independent enhancer far upstream of the human ‘‘beta- like globin’’ genes. Proc Natl Acad Sci U S A 86: 2554–2558. h59HS5 Is b-ACh Dispensable 25. Roseman RR, Pirrotta V, Geyer PK (1993) The su(Hw) protein insulates expression of the Drosophila melanogaster white gene from chromosomal position-effects. EMBO J 12: 435–442. 26. Zhou J, Barolo S, Szymanski P, Levine M (1996) The Fab-7 element of the bithorax complex attenuates enhancer-promoter interactions in the Drosophila embryo. Genes Dev 10: 3195–3201. 27. Capelson M, Corces VG (2006) SUMO conjugation attenuates the activity of the gypsy chromatin insulator. EMBO J 25: 1906–1914. 28. Chung JH, Whiteley M, Felsenfeld G (1993) A 59 element of the chicken beta- globin domain serves as an insulator in human erythroid cells and protects against position effect in Drosophila. Cell 74: 505–514. 29. Chung JH, Bell AC, Felsenfeld G (1997) Characterization of the chicken beta- globin insulator. Proc Natl Acad Sci U S A 94: 575–580. 30. Bell AC, West AG, Felsenfeld G (1999) The protein CTCF is required for the enhancer blocking activity of vertebrate insulators. Cell 98: 387–396. 31. Filippova GN, Fagerlie S, Klenova EM, Myers C, Dehner Y, et al. (1996) An exceptionally conserved transcriptional repressor, CTCF, employs different combinations of zinc fingers to bind diverged promoter sequences of avian and mammalian c-myc oncogenes. Mol Cell Biol 16: 2802–2813. 32. Vostrov AA, Quitschke WW (1997) The zinc finger protein CTCF binds to the APBbeta domain of the amyloid beta-protein precursor promoter. Evidence for a role in transcriptional activation. J Biol Chem 272: 33353–33359. 33. Splinter E, Heath H, Kooren J, Palstra RJ, Klous P, et al. (2006) CTCF mediates long-range chromatin looping and local histone modification in the beta-globin locus. Genes Dev 20: 2349–2354. 34. Yusufzai TM, Felsenfeld G (2004) The 59-HS4 chicken beta-globin insulator is a CTCF-dependent nuclear matrix-associated element. Proc Natl Acad Sci U S A 101: 8620–8624. 35. Drissen R, Palstra RJ, Gillemans N, Splinter E, Grosveld F, et al. (2004) The active spatial organization of the beta-globin locus requires the transcription factor EKLF. Genes Dev 18: 2485–2490. PLoS ONE | www.plosone.org 9 May 2008 | Volume 3 | Issue 5 | e2134