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IUPAC name 4-amino-5-methyl-3H-pyrimidin-2-one
CAS number 554-01-8
PubChem 65040
MeSH 5-Methylcytosine
Molecular formula C5H7N3O
Molar mass 125.129
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

5-Methylcytosine is a methylated form of cytosine in which a methyl group is attached to carbon 5, altering its structure without altering its base-pairing properties.


In vivo

5-Methylcytosine is an epigenetic modification formed by the action of DNA methyltransferases. Its function varies significantly among species:[1]

  • In bacteria, 5-methylcytosine can be found at a variety of sites, and is often used as a marker to protect DNA from being cut by native methylation-sensitive restriction enzymes.
  • In plants, 5-methylcytosine occurs at CpG, CpNpG and CpNpN sequences (where N = A, C or T).
  • In fungi and animals, 5-methylcytosine predominantly occurs at CpG dinucleotides. Although most eukaryotes methylate only a small percentage of these sites, in vertebrates 70-80% of CpG cytosines are methylated.

While spontaneous deamination of cytosine forms uracil, which is recognized and removed by DNA repair enzymes, deamination of 5-methylcytosine forms thymine. This conversion of a DNA base from cytosine (C) to thymine (T) can result in a transition mutation.

In vitro

5-Methylcytosine can be deaminated to form thymine with use of reagents such as nitrous acid; cytosine deaminates to uracil under similar conditions.

5-Methylcytosine is resistant to deamination by bisulfite treatment, which deaminates cytosine residues; this property is often exploited to analyze DNA cytosine methylation patterns with bisulfite sequencing.[2]

Additional images


  1. ^ Colot V, Rossignol JL (1999). "Eukaryotic DNA methylation as an evolutionary device". Bioessays 21 (5): 402-11. PMID 10376011.
  2. ^ Clark SJ, Harrison J, Paul CL, Frommer M (1994). "High sensitivity mapping of methylated cytosines". Nucleic Acids Res. 22 (15): 2990-7. PMID 8065911.
  • Griffiths, Anthony J. F. (1999). An Introduction to genetic analysis. San Francisco: W.H. Freeman, Chapter 15: Gene Mutation. ISBN 0-7167-3520-2.  (available online at the United States National Center for Biotechnology Information)
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "5-Methylcytosine". A list of authors is available in Wikipedia.
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