Conserved E boxes function as part of the enhancer in hypersensitive site 2 of the β-globin locus control region: Role of basic helix-loop-helix proteins

Laura Elnitski, Webb Miller, Ross Hardison

Research output: Contribution to journalArticle

72 Scopus citations

Abstract

The human β-globin gene cluster is regulated in part by a distal locus control region that is required for opening a chromatin domain in erythroid cells and enhancing expression of the β-like globin genes at the correct developmental stages. One part of the locus control region, called hypersensitive site 2 (HS2), functions as a strong enhancer. Matches to the consensus binding sites for basic helix-loop-helix (bHLH) proteins (E boxes) are well conserved within the HS2 core. We show that mutations of the HS2 core that alter an invariant E box cause a 3.5-fold reduction in enhancement of expression of an ε-globin reporter gene in transiently transfected K562 cells, both before and after induction. Mutations of the HS2 core that alter a less-highly conserved E box cause a more modest reduction in enhancement. Footprint analysis shows binding of erythroid nuclear proteins in vitro to the invariant E box as well as an adjacent CAC/GTG box. Probes containing the E box regions form sequence-specific complexes with proteins from both K562 and MEL nuclear extracts; these are disrupted by the same mutations that decrease enhancement. Some of these latter complexes contain known bHLH proteins, as revealed by specific loss of individual complexes when treated with antibodies against TALl and USF. Interaction between the E boxes and the bHLH proteins, as well as other binding proteins, could account for the role of these sites in enhancement by HS2.

Original languageEnglish (US)
Pages (from-to)369-378
Number of pages10
JournalJournal of Biological Chemistry
Volume272
Issue number1
DOIs
StatePublished - 1997

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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