 "cHS4" marks the border between the active euchromatin in the β-globin locus and the upstream heterochromatin region that is highly condensed and inactive.The "cHS4" insulator acts as both a barrier to chromatin-mediated silencing via heterochromatin spreading, and blocks interactions between enhancers and promoters.A distinguishing characteristic of "cHS4" is that it has a repetitive heterochromatic region on its 5' end.