CpG island, GC-rich element or GC box
Introduction
Non methylated segments of DNA containing the dinucleotide CpG at its expected frequency. [CpG dinucleotides are under-represented in bulk mammalian DNA & contain 5'-methyl-deoxycytosine.] CpG dinucleotides occur at only 20% of their expected frequency in bulk mammalian DNA. In certain regions, however, the density of CpG dinucleotides may increase to its expected frequency (5-10 fold). The islands take the form of stretches of DNA 1-2 kB long. There are approximately 45,000 CpG islands in the human genome. By restriction analysis, the islands are unmethylated. In many cases, the CpG islands begin just upstream (5' to) a promotor & extend downstream into the transcribed region of the gene before petering out. All housekeeping genes & 40% of tissue-restricted genes are associated with CpG islands. In the case of the latter, the CpG islands are unmethylated regardless of whether or not the gene is actively transcribed. Thus, unmethylated CpG islands may be necessary, but not sufficient for transcription. The islands may be a sign that the gene is potentially active, rather than inevitably transcribed. Methylation of a CpG island (5'-methyl-deoxycytosine) at a promotor usually prevents transcription. The SP1-binding site is a CpG island that binds the transcription factor Sp1.
More general terms
More specific terms
Additional terms
- CpG-binding protein; PHD finger & CXXC domain-containing protein 1; CXXC finger protein 1 (CXXC1, CGBP, PCCX1, PHF18)
- DNA methylation (promoter methylation)
References
- ↑ Watson et al (1986) Molecular Biology of the Gene, 4th ed, Benjamin/Cummings, Menlo Park, CA pg 696
- ↑ Kadonaga et al Science 242 1566 (1988)
- ↑ Salbaum et al EMBO J 7:2807 1988
- ↑ Molecular Cell Biology (2nd ed) Darnell J; Lodish H & Baltimore D (eds), Scientific American Books, WH Freeman, NY 1990, pg 292
- ↑ Antequera & Bird PNAS 90:11995 1993
- ↑ Genes VII, Lewis B., Oxford University Press, NY, 2000