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#nucleosome dynamics

2 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

Which nucleosome remodeling complex uses ATP hydrolysis?

Repositioning nucleosomes for regulated transcription demands mechanical force breaking 14 histone-DNA contacts. ATP-dependent chromatin remodelers couple ATP hydrolysis to translocate DNA around octamer. SWI/SNF family member containing SWI2/SNF2 ATPase domain hydrolyzes ATP sliding and evicting nucleosomes at promoters and enhancers, generating nucleosome depleted regions permitting preinitiation complex assembly. HAT and HDAC add or remove acetyl groups modulating charge not movement via ATP. DNMT methylates cytosine without remodeling. SWI/SNF mutations frequent in human cancers demonstrating tumor suppressor role maintaining accessibility. Thus ATP remodeling assigned to SWI/SNF complex specifically.

Ref: Vignali et al., 2000 Science; Alberts et al., Molecular Biology of the Cell, Chapter 4: SWI/SNF Uses ATP Hydrolysis

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