PMID:10391886
| Citation |
Jeltsch, A, Christ, F, Fatemi, M and Roth, M (1999) On the substrate specificity of DNA methyltransferases. adenine-N6 DNA methyltransferases also modify cytosine residues at position N4. J. Biol. Chem. 274:19538-44 |
|---|---|
| Abstract |
Methylation of DNA is important in many organisms and essential in mammals. Nucleobases can be methylated at the adenine-N6, cytosine-N4, or cytosine-C5 atoms by specific DNA methyltransferases. We show here that the M.EcoRV, M.EcoRI, and Escherichia coli dam methyltransferases as well as the N- and C-terminal domains of the M. FokI enzyme, which were formerly all classified as adenine-N6 DNA methyltransferases, also methylate cytosine residues at position N4. Kinetic analyses demonstrate that the rate of methylation of cytosine residues by M.EcoRV and the M.FokI enzymes is reduced by only 1-2 orders of magnitude in relation to methylation of adenines. This result shows that although these enzymes methylate DNA in a sequence specific manner, they have a low substrate specificity with respect to the target base. This unexpected finding has implications on the mechanism of adenine-N6 DNA methyltransferases. Sequence comparisons suggest that adenine-N6 and cytosine-N4 methyltransferases have changed their reaction specificity at least twice during evolution, a model that becomes much more likely given the partial functional overlap of both enzyme types. In contrast, methylation of adenine residues by the cytosine-N4 methyltransferase M.BamHI was not detectable. On the basis of our results, we suggest that adenine-N6 and cytosine-N4 methyltransferases should be grouped into one enzyme family. |
| Links | |
| Keywords |
Adenine/metabolism; Chromatography, High Pressure Liquid; Cytosine/metabolism; DNA-Cytosine Methylases/metabolism; Escherichia coli; Evolution, Molecular; Kinetics; Methylation; Oligodeoxyribonucleotides/chemistry; Site-Specific DNA-Methyltransferase (Adenine-Specific)/metabolism; Substrate Specificity |
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