Gene Regulation and Epigenetics · USMLE Step 1

Which epigenetic mark would you expect at the promoter region of an actively transcribed housekeeping gene?

  1. Dense CpG island methylation paired with H3K9 dimethylation
  2. Unmethylated CpG island with histone acetylation
  3. High levels of repressive H3K27 trimethylation (H3K27me3)
  4. Histone H2A ubiquitination marking transcriptional silencing
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Correct answer: Unmethylated CpG island with histone acetylation

Active housekeeping genes typically have unmethylated promoter CpG islands and acetylated histones — creating open chromatin (euchromatin) accessible to transcription machinery.

Difficulty: Medium Question 19 of 20

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