Locus control regions

Locus control regions (LCRs) are operationally defined by their ability to enhance the expression of linked genes to physiological levels in a tissue-specific and copy number–dependent manner at ectopic chromatin sites. Although their composition and locations relative to their cognate genes are different, LCRs have been described in a broad spectrum of mammalian gene systems, suggesting that they play an important role in the control of eukaryotic gene expression. The discovery of the LCR in the β-globin locus and the characterization of LCRs in other loci reinforces the concept that developmental and cell lineage–specific regulation of gene expression relies not on gene-proximal elements such as promoters, enhancers, and silencers exclusively, but also on long-range interactions of variouscis regulatory elements and dynamic chromatin alterations.