Histone Methylation: Chemically Inert but Chromatin Dynamic

Histone methylation is the modification of certain amino acids in a histone protein by the addition of one, two, or three methyl groups. In the cell nucleus, DNA is wound around histones. Methylation and demethylation of histones turns the genes in DNA "off" and "on,” respectively, either by loosening their tails, thereby allowing transcription factors and other proteins to access the DNA, or by encompassing their tails around the DNA, thereby restricting access to the DNA. This modification alters the properties of the nucleosome and affects its interactions with other proteins. Histone methylation is in general associated with transcriptional repression. However, methylation of some lysine and arginine residues of histones results in transcriptional activation. Posttranslational modifications (PTMs) have a significant role in cellular responses to both extrinsic and intrinsic factors. One of the most well studied PTMs is phosphorylation. The phospho-group carries a negative charge, which can influence confirmation or interactions. This chapter focuses on how this inert molecule can dramatically change the chromatin environment and, in turn, the survival or demise of an organism. Following this, it unveils the complexity and dynamics associated with the methylation of arginines and lysines within histone tails. It explores the specifics of the dynamic process of histone methylation. It also discusses the degree of methylation, which has specific consequences and explores the placement of methylated histones within the chromosomal environment that directly impacts different DNA templated processes.