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#acetyl groups

2 public questions tagged with this topic.

Eukaryotes gene regulation

Which enzyme removes acetyl groups during repression?

Histone acetylation neutralizes lysine epsilon-amino positive charge weakening DNA-histone interaction relaxing chromatin structure facilitating transcription factor access. Reversal mediated by histone deacetylases HDACs divided into Rpd3, Hda1, Sir2 families uses zinc or NAD as cofactors restoring positive charge promoting nucleosome compaction and repressive chromatin assembly. During glucose repression Tup1-recruited HDACs Rpd3L, Hda1 deacetylate H3K9, H3K18, H4K16 at GAL promoters preventing SAGA acetyltransferase Gcn5 access. Similarly at Saccharomyces telomeres Sir2 NAD-dependent HDAC deacetylates H4K16 enabling Sir3/Sir4 spreading and telomere position effect. HDAC activity antagonizes HATs establishing dynamic acetylation equilibrium regulating gene expression and heterochromatin maintenance precisely.

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 4: Histone Deacetylase HDAC Function in Repression

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Regulation of chromatin structure

Which enzyme removes acetyl groups from histones?

Histone acetylation neutralizes positive charge on lysine residues in flexible N-terminal tails, weakening interaction with negatively charged DNA and favoring open euchromatin. Histone deacetylases reverse this activation mark by hydrolyzing the N-acetyl amide bond, regenerating unmodified lysine. Loss of acetyl restores electrostatic attraction, tightening wrap around octamer and recruiting repressive complexes such as Sin3, NuRD and CoREST. Humans possess 18 HDAC enzymes divided into Zn2+-dependent classes I, II, IV and NAD+-dependent sirtuins, targeting both histone and non-histone substrates for transcriptional control.

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 4: Chromatin Structure, Histone Acetylation and Deacetylation

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