What is histone acetylation and how does it affect transcription?

• A. Histone acetylation reduces DNA-histone interactions, opens chromatin, and typically increases transcription.
• B. It degrades histones to allow transcription.
• C. Histone acetylation tightens chromatin, reducing transcription.
• D. It acts to recruit ribosomes during translation.

Answer: (A)

Histone acetylation is a modification where acetyl groups are added to lysine residues on histone tails by histone acetyltransferases. This neutralizes part of the histone’s positive charge, reducing its attraction to the negatively charged DNA. The result is a more open chromatin structure (euchromatin), which makes DNA more accessible to transcription factors and RNA polymerase, leading to increased transcription. Deacetylation reverses this, tightening the chromatin and generally reducing transcription. The idea that histone acetylation degrades histones or tightens chromatin, or that it recruits ribosomes for translation, doesn’t fit the mechanism or the process—acetylation modulates accessibility for transcription in the nucleus, not translation.