The eukaryotic genome is organized into clusters of coexpressed genes that tend to be transcribed coordinately at specific times throughout development and cell cycle, even though they may or may not be functionally related. The organization of eukaryotic genomes necessarily results in the proximity of domains with distinct functions. A domain containing genes that are transcriptionally active in a particular cell type might lie close to another domain containing genes that are not active. Insulators are multi-protein–DNA complexes that regulate the nuclear architecture. Chromatin insulators have been implicated in the regulation of high-order chromatin structure and may function to сompartmentalize the eukaryotic genome into independent domains of gene expression.