5-methylcytosine
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "5-methylcytosine".

5-Methylcytosine
IUPAC name	4-amino-5-methyl-3H-pyrimidin-2-one
Identifiers
CAS number	[554-01-8]
PubChem	65040
MeSH	5-Methylcytosine
SMILES	CC1=C(NC(=O)N=C1)N
Properties
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

Cytosine

References

1. ^ Colot V, Rossignol JL (1999). "Eukaryotic DNA methylation as an evolutionary device". Bioessays 21 (5): 402–11. doi:10.1002/(SICI)1521-1878(199905)21:5<402::AID-BIES7>3.0.CO;2-B. 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)