What is a transcriptional coactivator?

• A. A protein that binds DNA to repress transcription.
• B. A protein that degrades transcription factors.
• C. A protein that interacts with transcription factors to increase transcription without binding DNA directly.
• D. A protein that modifies tRNA during translation.

Answer: (C)

A transcriptional coactivator boosts gene expression by working with transcription factors and the transcription machinery without binding DNA itself. It acts as a bridge, linking DNA-bound transcription factors to RNA polymerase II and to other components of the transcription apparatus, and it often brings in tools that loosen or remodel chromatin (like histone modifiers) to make the DNA more accessible. Because it lacks a DNA-binding domain, it can’t recognize promoter sequences on its own; it relies on transcription factors already bound to DNA to recruit it to the right genes. This explains why it increases transcription without directly binding DNA.

Other descriptions don’t fit this role: a protein that binds DNA to repress transcription directly interacts with DNA and lowers transcription; a protein that degrades transcription factors affects their abundance rather than facilitating transcription; and a protein that modifies tRNA during translation acts in the translation stage, not transcription.