Correct option is B
Explanation-
Option B - Ubiquitination at specific lysine residues
Ubiquitination is a post-translational modification where a small protein called ubiquitin is attached to a lysine residue on a target protein, including histones. This process is mediated by enzymes - E1 (activating enzyme), E2 (conjugating enzyme) and E3 (ligase enzyme – gives substrate specificity)
Ubiquitination of histone H2A and H2B at lysine residues is strongly associated with DNA damage response. It regulates chromatin remodeling and recruitment of DNA repair proteins. Lysine is the only common site for ubiquitination due to its ε-amino group.
Incorrect options-
Option A - Phosphorylation at specific tyrosine residues
Phosphorylation relevant to DNA repair typically occurs on serine or threonine residues (e.g., phosphorylation of H2AX at Ser139 → γ-H2AX, a well-known DNA damage marker). Tyrosine phosphorylation is rare in histones and not a major player in DNA repair.
Option C - Acetylation at specific serine residues
Acetylation typically occurs at lysine residues, not serine. Lysine acetylation is indeed involved in DNA repair, but the question specifies serine, making this option inaccurate.
Option D - Methylation at specific serine residues
Like acetylation, methylation usually targets lysine and arginine residues, not serine. Methylation of H3K36 and H4K20 is known to be involved in DNA repair, but not serine methylation.
So, the correct answer is option B - Ubiquitination at specific lysine residues
