Expression results obtained with the chicken HS4 compound insulator. Plasmids are depicted to the left of their expression data generated in transiently transfected K562 cells. The control plasmids contain the promoter-only or the promoter with the HS2 enhancer. The 1.2-kb region of the cHS4 insulator was subcloned upstream of HS2 as a test of silencing. Deletions of the 3′ or 5′ ends of the cHS4 insulator, containing bases 1–450 or 450–1200 of the element, were also assessed for silencing. The FII region contains the 46-bp footprint region that binds CTCF. Positions of the fragments are shown relative to the full-length cHS4 sequence. The plasmid to test cHS4 in the EB position is the final plasmid in the image. The sizes of the DNA elements are for illustration only and are not drawn to scale.
