Transcription & Translation MCAT Practice Question
A 34-year-old woman with a family history of breast cancer undergoes genetic testing and is found to carry a BRCA1 mutation. Researchers studying her lymphocytes observe that a specific set of DNA repair genes normally shows elevated transcription due to histone H3 lysine 63 polyubiquitination (H3K63ub) at their promoters. However, when the cells are treated with an inhibitor of histone acetyltransferases (HATs), transcription of these DNA repair genes decreases to baseline levels despite persistent H3K63ub marks at the same promoters. Which of the following best explains why the elevated transcription of these DNA repair genes depends on both ubiquitination and acetylation marks?
Answer choices
- AHistone acetylation opens chromatin structure and provides docking sites for transcriptional co-activators, whereas H3K63ub alone recruits only architectural proteins that do not directly promote transcription initiationCorrect answer
- BH3K63ub activates histone deacetylases (HDACs), which must be inhibited by acetylation to prevent gene silencing
- CHistone acetylation is required to phosphorylate RNA polymerase II CTD, and H3K63ub serves only to stabilize the acetylation marks
- DH3K63ub recruits chromatin remodeling complexes that remove nucleosomes, while histone acetylation prevents re-nucleosome deposition during transcription elongation
- EHistone acetylation methylates DNA at the promoter, and H3K63ub prevents DNA methyltransferase recruitment to maintain an unmethylated state
- FH3K63ub independently recruits all necessary transcription factors, and acetylation serves only as a secondary epigenetic mark without functional contribution to transcription
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