Insulator

An insulator is a genetic boundary element that plays two distinct roles in gene expression, either as an enhancer-blocking element, or more rarely as a barrier against condensed chromatin proteins spreading onto active chromatin. The need for them arises where two adjacent genes on a chromosome have very different transcription patterns, and it is critical that the inducing or repressing mechanisms of one do not interfere with the neighbouring gene.

As an enhancer-blocking element
An insulator is a genetic boundary element that plays two distinct roles in gene expression, either as an enhancer-blocking element, or more rarely as a barrier against condensed chromatin proteins spreading onto active chromatin. The need for them arises where two adjacent genes on a chromosome have very different transcription patterns, and it is critical that the inducing or repressing mechanisms of one do not interfere with the neighbouring gene.[1]

Reference
Isolator (Genetik)