What is the effect of histone deacetylation on chromatin structure and transcription?

• A. It tightens chromatin and reduces transcription
• B. It loosens chromatin and increases transcription
• C. It has no effect on transcription
• D. It promotes transcription independent of chromatin

Answer: (A)

Deacetylation of histone tails tightens chromatin and reduces transcription. Removing acetyl groups from lysine residues on histone tails restores their positive charge, strengthening histone–DNA interactions and promoting a more condensed, less accessible chromatin state. When chromatin is compacted, RNA polymerase and transcription factors have a harder time accessing the DNA, leading to lower transcription. By contrast, acetylation loosens chromatin and is generally associated with active transcription, so deacetylation shifts the balance toward repression.