The PEG13 -DMR possesses insulator activity. The bars indicate the firefly luciferase expression relative to Renilla luciferase activity for constructs containing a 480 bp fragment encompassing the PEG13-DMR. As a control, the enhancer-blocking assay was also performed with inserts for the 5HS4 (1.2 kb insulator) or the II/III (‘core’ 5′HS4) of β-globin enhancer-blocker. The II/III mut construct is the core 5′HS4 fragment with mutated CTCF sites that abolish insulator activity. The constructs are illustrated at the top of the figure. Data are presented as fold-enhancer-blocking activity normalised to the reference pELuc vector.