Gene Regulation and Epigenetics · USMLE Step 1

Which of the following histone modifications is generally associated with opening chromatin and activating transcription?

  1. Histone H3 lysine 9 dimethylation (H3K9me2)
  2. Histone acetylation (e.g., H3 acetyl-lysine)
  3. Histone ubiquitination at H2A linked to repression
  4. Histone methylation at H3K27 associated with silencing
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Correct answer: Histone acetylation (e.g., H3 acetyl-lysine)

Histone acetylation neutralizes positive charges on histones, reduces histone-DNA interaction, de-condenses chromatin (euchromatin), and thereby facilitates transcription activation.

Difficulty: Medium Question 4 of 20

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