Locus control region

The locus control region (LCR) is a genetic control region that controls the activity of a gene region. LCRs are called DNase-sensitive regions. These are assumed to have an "open" chromatin structure. In this "open" chromatin structure, the DNA is cleared of histones so that transcription factors can bind to this DNA region.

The concept of locus control regions is based on the observation that the tissue-specific regulation of gene expression during embryonic development as well as in the adult organism is not only based on regulatory elements close to the nucleus (such as promoter, enhancer, silencer), but also on interactions with regulatory elements located further away on the same chromosome.

Locus control regions increase the expression of whole gene clusters in a cell-typical way. In addition to binding sites for transcription factors, they obviously also have an influence on the chromatin structure in the corresponding region.

Promoter regions are located towards the 5'-end in front of the gene. RNA polymerases bind to these sites to catalyze gene transcription.

Enhancer regions are located either in front or behind the gene. They are important for the tissue-specific regulation of protein gene expression and the regulation of the synthesis of the different protein chains.

LRCs as important controls of gene expression can be located many thousands of base pairs away from the actual site of transcription. How these long distances within the genome are bridged is still hypothetical. Finally, different models are discussed:

looping model. The LCR sequence of the DNA forms a loop which physically approaches the gene region to be transcribed. By this physical approximation, the LCR sequence can influence the transcription of the gene.

Along the loop: In the so-called "along the loop" procedure, the complex of LCR and bound factors travels along the DNA until it recognizes the corresponding promoter region.

LCRs are particularly well described in the beta-globulin group. However, they are not restricted to this gene group. In humans > 20 gene families are known whose gene activities are controlled by LCRs.