The chicken β-globin 5'HS4 boundary element blocks enhancer-mediated suppression of silencing

Mark C. Walters, Steven Fiering, Eric E. Bouhassira, David Scalzo, Scott Goeke, Wendy Magis, David Garrick, Emma Whitelaw, David I.K. Martin

Research output: Contribution to journalArticlepeer-review

50 Scopus citations


A constitutive DNase I-hypersensitive site 5' of the chicken β-globin locus, termed 5'HS4 or cHS4, has been shown to insulate a promoter from the effect of an upstream enhancer and to reduce position effects on mini-white expression in Drosophila cells; on the basis of these findings, it has been designated a chromatin insulator. We have examined the effect of the cHS4 insulator in a system that assays both the level of gene expression and the rate of transcriptional silencing. Because transgenes flanked by insulator elements are shielded from position effects in Drosophila cells, we tested the ability of cHS4 to protect transgenes from position effects in mammalian cells. Flanking of an expression vector with the cHS4 insulator in a colony assay did not increase the number of G418-resistant colonies. Using lox/cre- based recombinase-mediated cassette exchange to control integration position, we studied the effect of cHS4 on the silencing of an integrated β-geo reporter at three genomic sites in K562 erythroleukemia cells. In this assay, enhancers act to suppress silencing but do not increase expression levels. While cHS4 blocked enhancement at each integration site, the strength of the effect varied from site to site. Furthermore, at some sites, cHS4 inhibited the enhancer effect either when placed between the enhancer and the promoter or when placed upstream of the enhancer. These results suggest that the activity of cHS4 is not dominant in all contexts and is unlikely to prevent silencing at all genomic integration sites.

Original languageEnglish (US)
Pages (from-to)3714-3726
Number of pages13
JournalMolecular and cellular biology
Issue number5
StatePublished - May 1999

ASJC Scopus subject areas

  • Molecular Biology
  • Cell Biology


Dive into the research topics of 'The chicken β-globin 5'HS4 boundary element blocks enhancer-mediated suppression of silencing'. Together they form a unique fingerprint.

Cite this