Question

Describe roles of Histone Modifications and give two examples of the most common Histone Modifications (chemical group and histone residue) and their functional roles on gene expression.​

Answer 1

A histone modification is a covalent post-translational modification (PTM) to histone proteins which includes methylation, phosphorylation, acetylation, ubiquitylation, and sumoylation. The PTMs made to histones can impact gene expression by altering chromatin structure or recruiting histone modifiers. Histone proteins act to package DNA, which wraps around the eight histones, into chromosomes. Histone modifications act in diverse biological processes such as transcriptional activation/inactivation, chromosome packaging, and DNA damage/repair.

Role of Histone Acetylation/Deacetylation

• The process of histone acetylation is tightly involved in the regulation of many cellular processes including chromatin dynamics and transcription, gene silencing, cell cycle progression, apoptosis, differentiation, DNA replication, DNA repair, nuclear import, and neuronal repression.
• Examples : Acetylation of the 27th lysine residue in H3 histone leads to its activation of transcription.

Role of Histone methylation/Demethylation

• In the cell nucleus, when histone methylation occurs, specific genes within the DNA complexed with the histone may be activated or silenced.
• Example : Mono-methylation of 4th lysine residue of H3 is found at transcriptional enhancers; Tri-methylation of 4th lysine residue of H3 ia found at gene promoters.