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#histone marks

3 public questions tagged with this topic.

Regulation of chromatin structure

Which histone modification loosens DNA-histone interaction?

Lysine acetylation directly weakens histone-DNA electrostatic attraction. Transfer of acetyl from acetyl-CoA to ε-amino group removes positive charge, reducing net basic character of tail and diminishing binding to phosphate backbone. Structural studies reveal increased tail disorder, enhanced nucleosome breathing and greater accessibility for transcription factors. Bromodomain proteins further recognize acetyl-lysine, recruiting remodelers that slide or eject nucleosomes. Functionally, hyperacetylation at promoters and enhancers correlates with euchromatin formation, while deacetylation restores compaction. This biophysical effect distinguishes acetylation from methylation that preserves charge.

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 8: Acetylation Loosens DNA-Histone Interaction, Chromatin Opening

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Regulation of chromatin structure

Bromodomains specifically recognize which histone modification?

Effector proteins interpreting histone code contain specific reader modules. Bromodomain, originally identified in Drosophila Brahma chromatin remodeling complex, forms four-helix bundle with deep hydrophobic pocket specifically accommodating acetyl-lysine side chain, preferentially H3K14ac, H3K27ac, H4K16ac. Binding recruits transcription initiation factor TFIID, SWI/SNF remodeler and p300 acetyltransferase to acetylated active chromatin stimulating gene expression. Chromodomains recognize methyllysine, 14-3-3 binds phosphoserine, no specialized domain uniquely recognizes ubiquitin alone. Bromodomain inhibition by small molecule JQ1 displaces readers blocking oncogenic transcription and inflammation, highlighting therapeutic importance for active chromatin.

Ref: Dhalluin et al., Nature 1999 Bromodomain Structure; Lodish et al., Chapter 8: Bromodomains Recognize Acetylated Lysine

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Eukaryotic chromatin and chromosome

H3K9 methylation marks:

Histone code marks specific chromatin states. H3 lysine 9 di and trimethylation catalyzed by SUV39H1 and SUV39H2 methyltransferases creates high affinity binding site for heterochromatin protein 1 alpha via its chromodomain, inducing spreading, compaction and transcriptional repression. H3K9 trimethylation enriched at pericentric satellite repeats, subtelomeric repeats and retrotransposons characterizes constitutive heterochromatin, contrasting with H3K4 trimethylation at active promoters. HP1 oligomerization and interaction with DNMTs maintain domain stability. Disruption causes position effect variegation, ectopic transcription and chromosome missegregation defects compromising genome stability severely.

Ref: Bannister et al., Nature 2001; Lodish et al., Molecular Cell Biology, 9th ed., Chapter 8: H3K9 Methylation Heterochromatin Mark

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