An Intergenic region is a stretch of DNA sequences located between genes. Intergenic regions are a subset of noncoding DNA. Occasionally some intergenic DNA acts to control genes nearby, but most of it has no currently known function. It is one of the DNA sequences sometimes referred to as junk DNA, though it is only one phenomenon labeled such and in scientific studies today, the term is less used. Recently transcribed RNA from the DNA fragments in intergenic regions were known as "dark matter" or "dark matter transcripts".
Properties
Intergenic regions are different from intragenic regions, which are short, non-coding regions that are found within genes, especially within the genes of eukaryotic organisms. According to the ENCODE project's study of the human genome, due to "both the expansion of genic regions by the discovery of new isoforms and the identification of novel intergenic transcripts, there has been a marked increase in the number of intergenic regions due to their fragmentation and a decrease in their lengths " Scientists have now artificially synthesized proteins from intergenic regions.
Functions
Historically intergenic regions have sometimes been called junk DNA suggesting that they have no function. However, it has been known for a long time that these regions do contain functionally important elements such as promoters and enhancers. In particular, intergenic regions often contain enhancer DNA sequences, which can activate expression of discrete sets of genes over distances of several thousand base pairs. Changes in the proteins bound on enhancers reprogram gene expression and affect the cell phenotype. Also intergenic regions may contain as yet unidentified genes such as noncoding RNAs. Though little is known about them, they are thought to have regulatory functions. In recent years the ENCODE project has been studying intergenic regions in humans in more detail.
Intergenic regions in organisms
In humans, intergenic regions comprise about 50% of the genome, whereas this number is much less in bacteria and yeast In Plasmodium falciparum, many intergenic regions have an AT content of 90%
