Histone modification- Acetylation, Methylation and Phosphorylation

Histone modifications are covalent chemical changes that occur on the N-terminal tails of histone proteins. These modifications regulate chromatin structure and gene expression without altering the DNA sequence. Important Examples 1. Histone Acetylation Neutralizes the positive charge of lysine residues. Weakens histone-DNA interaction. DNA becomes more accessible to transcription factors. Result: Increased gene expression. 2. Histone Methylation Effect depends on the amino acid residue modified. H3K4me3 → Gene activation. H3K9me3 and H3K27me3 → Gene repression. 3. Histone Phosphorylation Important during mitosis. Associated with chromosome condensation. Participates in DNA damage response. 4. Histone SUMOylation Addition of SUMO proteins to lysine residues. Recruits transcriptional repressors and HDACs. Result: Gene silencing and chromatin condensation.