Question

Common covalent modifications in core histone proteins include:
(A) Acetylation
(B) Methylation
(C) Phosphorylation
(D) ADP-ribosylation
Choose the correct answer from the options given below:

• A. (B), (C) and (D) only.
• B. (A), (B) and (D) only.
• C. (A), (B), (C) and (D).
• D. (A), (C) and (D) only.

Hint:

Histone modifications are diverse and include Acetylation, Methylation, Phosphorylation, Ubiquitination, and ADP-ribosylation.
When asked to identify valid modifications, almost all major cellular chemical groups (acetyl, methyl, phosphoryl, ADP-ribosyl) are correct.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Histones are highly alkaline proteins around which DNA winds to form nucleosomes.
Core histones (H2A, H2B, H3, H4) undergo post-translational modifications (PTMs) primarily on their flexible N-terminal tails.
These modifications regulate chromatin structure and gene transcription (the "histone code").

Step 2: Detailed Explanation:
The flexible tails of core histones are subject to several reversible covalent modifications:
- Acetylation (A): Occurs on lysine residues, neutralizes positive charges, and generally relaxes chromatin to activate transcription.
- Methylation (B): Occurs on lysine and arginine residues, acting as an activation or repression signal depending on the specific site.
- Phosphorylation (C): Occurs on serine, threonine, and tyrosine residues, often associated with chromosome condensation during mitosis and transcriptional activation.
- ADP-ribosylation (D): The addition of ADP-ribose units to glutamate or lysine residues, which plays an important role in the DNA damage response and DNA repair.
Thus, all four are common covalent modifications of core histones.

Step 3: Final Answer:
The correct answer is (A), (B), (C) and (D), corresponding to option (C).