Which of the following histone tail modifications is most likely to cause closed chromatin?

• A. Acetylation
• B. Methylation
• C. Phosphorylation
• D. Ubiquitination

Answer: (B)

Verified step by step guidance

1. Understand the role of histone tail modifications in chromatin structure. Histone modifications can either open (euchromatin) or close (heterochromatin) chromatin, affecting gene expression.
2. Recognize that acetylation of histone tails generally leads to an open chromatin structure. This is because acetylation neutralizes the positive charge on histones, reducing their affinity for the negatively charged DNA, thus loosening the chromatin.
3. Identify that methylation of histone tails can lead to either open or closed chromatin, depending on the specific amino acid residues that are methylated and the number of methyl groups added. However, certain methylation patterns, such as trimethylation of histone H3 at lysine 9 (H3K9me3), are associated with closed chromatin and gene silencing.
4. Consider phosphorylation, which can have varied effects on chromatin structure. It often plays a role in signaling pathways and can lead to either chromatin condensation or relaxation, depending on the context.
5. Ubiquitination typically marks proteins for degradation but can also influence chromatin structure. However, it is less directly associated with chromatin condensation compared to methylation.