Intergenic region

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Illustration of intergenic DNA

An Intergenic region (IGR) is a stretch of DNA sequences located between genes.[1] 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 DNA fragments in intergenic regions were known as "dark matter" or "dark matter transcripts".[2]

Properties

Intergenic regions are different from intragenic regions (or introns), 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 (from 32,481 to 60,250) due to their fragmentation and a decrease in their lengths (from 14,170 bp to 3,949 bp median length)"[3]

Scientists have now artificially synthesized proteins from intergenic regions.[4]

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. 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.[5][6]

Intergenic regions in organisms

In humans, intergenic regions comprise about 80%-90% of the genome, whereas this number is much less in bacteria (15%) and yeast (30%) [7]

In Plasmodium falciparum, many intergenic regions have an AT content of 90% [8]

See also

References

  1. ↑ Tropp, Burton E. (2008). Molecular Biology: Genes to Proteins. Jones & Bartlett Learning. ISBN 9780763709167. 
  2. ↑ van Bakel, H; Nislow, C; Blencowe, BJ; Hughes, TR (2010 May 18). "Most "dark matter" transcripts are associated with known genes.". PLoS Biology 8 (5): e1000371. doi:10.1371/journal.pbio.1000371. PMC 2872640. PMID 20502517. 
  3. ↑ Djebali S; Davis CA; Merkel A et al. (September 2012). "Landscape of transcription in human cells". Nature 489 (7414): 101–8. doi:10.1038/nature11233. PMID 22955620. 
  4. ↑ Dhar, P. K.; Thwin, C.; Tun, K.; Tsumoto, Y.; Maurer-Stroh, S.; Eisenhaber, F.; Surana, U. (2009). "Synthesizing non-natural parts from natural genomic template". Journal of Biological Engineering 3: 2. doi:10.1186/1754-1611-3-2. PMC 2642765. PMID 19187561. 
  5. ↑ Birney E; Stamatoyannopoulos JA; Dutta A et al. (June 2007). "Identification and analysis of functional elements in 1% of the human genome by the ENCODE pilot project". Nature 447 (7146): 799–816. doi:10.1038/nature05874. PMC 2212820. PMID 17571346. 
  6. ↑ Dunham I; Kundaje A; Aldred SF et al. (September 2012). "An integrated encyclopedia of DNA elements in the human genome". Nature 489 (7414): 57–74. doi:10.1038/nature11247. PMID 22955616. 
  7. ↑ Shabalina, SA; Ogurtsov, AY; Kondrashov, VA; Kondrashov, AS (2001 Jul). "Selective constraint in intergenic regions of human and mouse genomes.". Trends in genetics : TIG 17 (7): 373–6. PMID 11418197. 
  8. ↑ Gardner, Malcolm; Hall, N; Fung, E; White, O; Berriman, M; Hyman, RW; Carlton, JM; Pain, A et al. (3 October 2002). "Genome sequence of the human malaria parasite Plasmodium falciparum". Nature 419 (6906): 498–511. doi:10.1038/nature01097. PMID 12368864. 

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