DNA methylation, histone code, chromatin remodeling, X-inactivation, imprinting.
Epigenetics And Chromatin
Epigenetics
Heritable changes in gene expression not caused by DNA sequence change. Mediated by DNA methylation, histone modifications, chromatin…
DNA methylation (5mC)
Covalent methyl group on cytosine C5, primarily in CpG dinucleotides in mammals. Written by DNMT3A/B (de novo) + DNMT1 (maintenance); read…
CpG island
~500-2000 bp region with elevated CpG frequency (>50%) and lower methylation, commonly at promoters of ~70% of mammalian genes. Aberrant…
Histone post-translational modification
Covalent tags on histone tails (H3/H4 Lys/Arg/Ser): acetylation, methylation, phosphorylation, ubiquitination, SUMOylation. Form a 'histone…
H3K4me3
Trimethylation of H3 Lys4 — active-promoter mark. Written by SET1/MLL; bound by TAF3/CHD1 (PHD, chromo). Rare at repressed genes; bivalent…
H3K27me3
Trimethylation of H3 Lys27 — Polycomb-mediated silencing mark. Written by PRC2 (EZH2 catalytic); read by PRC1 (CBX). Broad repression of…
Histone acetylation
Lysine acetylation (Kac) by HATs (p300, CBP, GCN5) neutralises positive charge, loosens chromatin, recruits bromodomain readers (BET…
X-chromosome inactivation
Dosage-compensation mechanism in female mammals: one of two X chromosomes randomly silenced per cell via XIST lncRNA-mediated spreading of…
Genomic imprinting
Parent-of-origin-specific silencing via differentially methylated regions (DMRs) set in the germline. ~100 imprinted loci in mammals;…
Chromatin remodeller
ATP-dependent complexes (SWI/SNF, ISWI, CHD, INO80) slide or eject nucleosomes. Frequently mutated in cancer (SMARCA4, ARID1A). Regulates…