Evidence that DNase I hypersensitive site 5 of the human β-globin locus control region functions as a chromosomal insulator in transgenic mice

We have previously reported that DNase I hypersensitive site 5 (5′HS5) of the human β-globin locus control region functions as a chromatin insulator in stable transfection assays. In this report we show that a 3.2 kb DNA fragment containing the entire 5′HS5 region can protect a position-sensitive (A)γ-globin gene against position effects in transgenic mice. Bracketing is required for function of 5′HS5 as an insulator. The 5′HS5 insulator operates in adult as well as in embryonic murine erythroid cells. The insulator has no significant stimulatory effects of its own. These results indicate that 5′HS5 can function as a chromatin insulator in vivo.