Which statement best describes how chromatin remodeling influences transcription?

Which statement best describes how chromatin remodeling influences transcription?

• A. Promoters are always accessible regardless of chromatin state.
• B. Nucleosome formation always enhances transcription.
• C. Histone modifications do not affect DNA accessibility.
• D. Chromatin remodeling and histone modifications can modulate promoter accessibility.

Answer: (D)

Access to genes is controlled by how tightly the DNA is packaged in chromatin, especially around promoter regions. Chromatin remodeling changes where and how nucleosomes sit on the DNA, which can expose promoters so the transcription machinery can bind and initiate transcription, or cover them and repress transcription. Histone modifications add another layer of control by altering the interaction between DNA and histones and by recruiting other proteins that promote a more open or a more closed chromatin state. When remodeling plus histone marks shift the promoter from a closed, inaccessible state to an open, accessible one, transcription can proceed more readily; they can also do the opposite to repress transcription. This is precisely what statement describing chromatin remodeling and histone modifications as modulating promoter accessibility captures. The other ideas don’t fit: promoters aren’t always accessible regardless of chromatin state, because packaging can block access; nucleosome formation does not always boost transcription—in many cases it represses it by hindering access; and histone modifications do affect DNA accessibility through changing chromatin structure and recruiting factors that alter openness.

Access to genes is controlled by how tightly the DNA is packaged in chromatin, especially around promoter regions. Chromatin remodeling changes where and how nucleosomes sit on the DNA, which can expose promoters so the transcription machinery can bind and initiate transcription, or cover them and repress transcription. Histone modifications add another layer of control by altering the interaction between DNA and histones and by recruiting other proteins that promote a more open or a more closed chromatin state. When remodeling plus histone marks shift the promoter from a closed, inaccessible state to an open, accessible one, transcription can proceed more readily; they can also do the opposite to repress transcription.

This is precisely what statement describing chromatin remodeling and histone modifications as modulating promoter accessibility captures. The other ideas don’t fit: promoters aren’t always accessible regardless of chromatin state, because packaging can block access; nucleosome formation does not always boost transcription—in many cases it represses it by hindering access; and histone modifications do affect DNA accessibility through changing chromatin structure and recruiting factors that alter openness.