Upstream element of the sea urchin arylsulfatase gene serves as an insulator

Insulator DNAs functionally isolate neighboring genes by blocking interactions between distal cis-regulatory elements and promoters. Here we report that a DNA fragment located in the upstream region of sea urchin, H. pulcherrimus, arylsulfatase (HpArs) gene blocks the interaction of the Ars enhancer when positioned between the enhancer and the target promoter, in an orientation dependent manner. The Ars insulator works only 3' to 5' direction and has no significant stimulatory or inhibitory effects on its own promoter. In transgenic Drosophila, the Ars insulator blocks the interaction between even-skipped stripe enhancer and its target promoter. The insulation mechanism operates also unidirectionally in Drosophila. We also show that the efficiency of transformation of HeLa cells is enhanced when the integrated gene is flanked by the Ars insulator, suggesting the sea urchin insulator overcomes the position-dependent transgene expression in mammalian cells. These results demonstrate that the mechanism of action of the insulator has been conserved throughout evolution.