Which histone modification involves adding methyl groups to histone proteins and affects chromatin compaction?

Which histone modification involves adding methyl groups to histone proteins and affects chromatin compaction?

• A. Histone acetylation
• B. DNA methylation
• C. Histone methylation
• D. Ubiquitination

Answer: (C)

Histone methylation is the process of adding methyl groups to histone proteins, and it helps determine how tightly the DNA is wound around histones. Depending on the residue and the methylation state (mono-, di-, or tri-methylation), this mark can recruit proteins that compact chromatin, forming heterochromatin and making genes less accessible. For example, certain methyl marks such as H3K9me3 or H3K27me3 promote a more condensed chromatin state. This contrasts with histone acetylation, which adds acetyl groups to histones and loosens DNA–histone interactions to relax chromatin and often activate transcription. DNA methylation is a separate modification on DNA itself, not histones, and uses DNA methyltransferases. Ubiquitination attaches a protein tag rather than a methyl group, altering chromatin dynamics in another way. So the modification that specifically involves adding methyl groups to histones and can affect chromatin compaction is histone methylation.

Histone methylation is the process of adding methyl groups to histone proteins, and it helps determine how tightly the DNA is wound around histones. Depending on the residue and the methylation state (mono-, di-, or tri-methylation), this mark can recruit proteins that compact chromatin, forming heterochromatin and making genes less accessible. For example, certain methyl marks such as H3K9me3 or H3K27me3 promote a more condensed chromatin state. This contrasts with histone acetylation, which adds acetyl groups to histones and loosens DNA–histone interactions to relax chromatin and often activate transcription. DNA methylation is a separate modification on DNA itself, not histones, and uses DNA methyltransferases. Ubiquitination attaches a protein tag rather than a methyl group, altering chromatin dynamics in another way. So the modification that specifically involves adding methyl groups to histones and can affect chromatin compaction is histone methylation.