DNA G-quadruplex structures act as functional elements in α- and β-globin enhancers.

BACKGROUND: Enhancer elements interact with target genes at a distance to modulate their expression, but the molecular details of enhancer-promoter interaction are incompletely understood. G-quadruplex DNA secondary structures (G4s) have recently been shown to co-occur with 3D chromatin interactions; however, the functional importance of G4s within enhancers remains unclear. RESULTS: In this study, we identify novel G4 structures within two locus control regions at the human α- and β-globin loci. We find that mutating G4 motifs by genome editing prevents their folding into G4 structures in cells and disrupts 3D enhancer-promoter interactions and target gene expression in a manner comparable to whole enhancer deletion. Furthermore, restoration of G4 structure formation using a dissimilar G4-forming primary sequence recovers specific enhancer-gene interactions and gene expression. Through proteomic, biophysical, and genomic profiling, we find that enhancer G4s are tightly linked to the maintenance of an active chromatin state and RNA polymerase II recruitment to regulate target gene expression. CONCLUSIONS: Our study shows that folded G4 structures can act as functional elements that mediate 3D enhancer-promoter interactions to support enhancer-driven globin gene regulation.