Relationships between DNA and Histone Modifications

Epigenetics is often defined as a memory mechanism that imposes additional structural and functional information on gene sequences without affecting the primary nucleotide sequence itself. In mammalian cells, DNA methylation at CpG dinucleotides and histone posttranslational modifications are key aspects of this epigenetic code. DNA cytosine methylation and modifications on histone tails have their specific functional meanings and are interpreted by interacting proteins that act as readers of the epigenetic code. However, what is often observed is that DNA and histone modifications do not occur independently but are linked to each other forming a complex network of mutual positive and negative crosstalk interactions. In this review, we focus on the interdependence of DNA methylation and histone modifications, with emphasis on histone acetylation and methylation of histone H3 at lysines 4, 9, 27, and 36.