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Methyltransferases

DNA methyltrasferases

DNA methyltransferases are enzymes which methylate DNA spicifically. Here DNA methyltransferases from restriction-modification systems (RM systems) are studied. RM system is used by bacteria and archeae to protect themselves from foreign DNA, such as the one borne by bacteriophages. They consist of endonucleases (restriction enzymes), which specifically cleave foreign DNA, and methyltransferses, which protect host DNA by methylating target sites.
A number of DNA methyltaransferase classifications exist.
1)By methylation type.
DNA methyltransferses have 3 types of methylation dependin on which atom is methylated:
- m6a (6th atom of adenine)
- m4c (4th atom of cytosine)
- m5c (5th atom of cytosine)
In fact both m6a and m4c DNA methyltransferases methylate nitrogen and have a lot in common, while DNA methyltransferases m5c methylate carbon and drammaticallu different by sequence.

2) By motif groups.
There are 10 (I, II, III, IV, VI, VII, VIII, IX, X)DNA methyltransferase motifs found (Malone, 1991).All of them are included in DNA methyltransferase domain.
Another component of the domain is a DNA recognition sequence named TRD (Target recognition domain). Sometimes TRD might be abscent and a special protein named subunit S is synthetyzed for DNA recognition nstead (see classofication by RM system types).
Depending on consequence of the DNA methyltransferase motifs and TRD DNA methyltarnsferases are divided into 3 main groups:

- I-II-III-IV-V-VI-VII-VIII-TRD-IX-X	C5
- X-I-II-III-TRD-IV-V-VI-VII-VIII	Alpha
- IV-V-VI-VII-VIII-TRD-X-I-II-III	Beta
- X-I-II-III-IV-V-VI-VII-VIII-(TRD)	Gamma (TRD is abscent in DNA methyltransferases from Type I RM systems)

All the C5 DNA methyltransferses have m5c type of methylation and all m5c DNA methyltarnsferses belong C5 motif group. The rest motif groups are spread among all the other types of methylation.

3)By type of RM system it belongs to.
There are 4 (I,II,III,IV) types of RM systems known, classidied mainly by subunit composition. Three of them (I, II and III) include methyltransferases. In RM systems However, orphan (or somewhere so-called solitary) methyltransferses

Service for defining input DNA-methyltrasferase domain class by HMM-profiles.	Web service MTPro
Distribution of DNA-methyltransferes classes among bacterial and archeal phyla and econiches.	Download Excel file