How does histone methylation control gene expression?

Histone methylation, first discovered in 1964, is a relatively stable post-translational modification (PTM) type, which derived from the interaction between the protein side chain with S-adenosyl methionine (SAM). This epigenetic modification, catalyzed by histone methyltransferases (HMTs), can occur at various sites of histones, but mainly occurs at the N-terminal lysine and arginine residues of H3 and H4, and it can be controlled by multiple positive and negative regulatory proteins to activate or inhibit transcription. This PTM is a very important and widespread chromatin modification that regulates gene expression by affecting the precise integration of chromatin or signal transduction, thereby affecting a variety of physiological processes in cells. The methylation of histones is reversible, and a considerable number of HMTs and histone demethylases (HDMs) have been identified, which jointly participate in mediating the methylation and demethylation of histones.

Explanation:

https://www.creativebiomart.net/epigenetics/category/products/proteins-enzymes/histone-modification-proteins/histone-methylation-proteins/

enzyme speed up the reactions