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Nature Structural & Molecular Biology 15, 1003–1004 (1 October 2008) | doi:10.1038/nsmb1008-1003

Reading and writing DNA methylation

Albert Jeltsch

In mammalian DNA, about 70% of the cytosine residues within CG sequences are methylated at the cytosine-C5 position in a cell type–specific pattern. Methylation of CG-rich sequences in the promoter regions of genes, so-called CG islands, represses gene expression and represents an important epigenetic signal that is essential for development.