ABSTRACT
The greater part of the DNA methylation (80%) is found on the cytosine of CpG dinucleotides, which are distributed throughout the genome but are also found concentrated in regions known as CpG islands. Methylation of histone H3 lysine 4 (H3K4) has been suggested to protect gene promoters from de novo DNA methylation in somatic cells. Because of the interaction between DNMT3L and the histone H3 N-terminal tail, the mammalian de novo DNA methylation machinery may be able to translate patterns of H3K4 methylation, which are not themselves preserved during chromosome replication, into heritable patterns of DNA methylation that mediate transcriptional silencing of the affected sequences. The types of epigenetic modification that proteins control are quite different from those controlled by DNA methylation, but they are just as important for regulating the structure of the nucleosomes that controls access to the information contained in the underlying DNA sequence.
