New Frontiers in Epigenetic Modifications

In multicellular eukaryotes, DNA methylation is associated with transcriptional silencing [3]. In these organisms, DNA methylation has been observed exclusively on the C5 position of the cytosine ring and is frequently found in CpG-rich regions. This process is attributed to the action of DNA methyltransferases (DNMTs), which utilize the cofactor, S-adenosyl-L-methionine. Approximately half of all human genes have CpG islands in their promoter regions but these stretches of DNA are typically 

Transcriptional repression by DNA methylation is achieved by various modes of action. In one such mechanism, DNA methylation simply inhibits the binding of a transcription factor [17[. By a more complex means of action, a number of DNA methyl-binding proteins potentiate transcriptional silencing. In some cases, binding is accompanied by the action of an associated histone-modifying enzyme. 

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