The following statements were made regarding the roles of histone modifications in transcriptional regulation:

A. Acetylation of histones is generally associated with transcriptional repression by making the chromatin more compact.
B. Methylation of histones can either activate or repress transcription depending on the specific residue modified.
C. Phosphorylation of histones occurs in response to DNA damage and can influence gene expression.
D. Histone modifications influence the recruitment of RNA polymerase complex but not transcription factors.

Which one of the following options represents the combination of all correct statements?

Correct option is B

Explanation:

• A is incorrect: Histone acetylation activates transcription by loosening chromatin structure, not repressing it. Acetyl groups neutralize positive charges on histones, reducing DNA-histone interactions and making chromatin more open.

• B is correct: Histone methylation can activate or repress transcription depending on the residue (e.g., H3K4 methylation activates, H3K9 methylation represses).

• C is correct: Histone phosphorylation occurs in response to DNA damage and other signals, modulating gene expression.

• D is incorrect: Histone modifications influence recruitment of both RNA polymerase complexes and transcription factors by altering chromatin accessibility and providing binding sites.

Information Booster:

• Histone acetylation by histone acetyltransferases (HATs) is a hallmark of active transcription.

• Methylation effects depend on site and degree of methylation; e.g., trimethylation at H3K4 is activating, at H3K27 is repressive.

• Phosphorylation is involved in signaling pathways including DNA damage repair and chromatin remodeling.

• Histone modifications create a "histone code" that is read by proteins including transcription factors and RNA polymerase machinery.