CpG island
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CpG islands are regions of DNA near and in approximately 40% of promoters of mammalian genes. They are regions where a large concentration of phosphodiester-linked cytosine and guanine pairs exist. The "p" in CpG represents that they are phosphodiester-linked. Unlike CpG sites in the coding region of a gene, in most instances, the CpG sites in the CpG islands are unmethylated if genes are expressed. This observation led to the speculation that methylation of CpG sites in the promoter of a gene may inhibit the expression of a gene.
The usual formal definition of a CpG island is a region with at least 200 bp and with a GC percentage that is greater than 50% and with an observed/expected CpG ratio that is greater than 0.6. 82% of all Not 1 sites are found in these islands.Majority are associated with genes or recognition sites for restriction enzymes.
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- Fatemi, M, Pao, MM, Jeong, S, Gal-Yam, EN, Egger, G, Weisenberger, DJ, Jones, PA. (November Nov 27;33(20):e176.). "Vectors and delivery systems in gene therapy". Medical Science Monitor 33 (20). PMID 16314307. Retrieved on 2006-06-28.
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