What is a transcriptional activator?

• A. A protein that binds DNA to block transcription
• B. A protein that binds DNA to recruit RNA polymerase and activate transcription
• C. A molecule that degrades RNA
• D. A protein that binds DNA to recruit transcriptional machinery and enhance transcription

Answer: (D)

Transcriptional activators are DNA-binding proteins that increase gene transcription by helping assemble the transcriptional machinery at regulatory DNA elements. They bind to enhancers or promoter-proximal regions and recruit components such as Mediator, coactivators, chromatin remodelers, and RNA polymerase II to boost transcription. The choice that describes a protein binding DNA to recruit transcriptional machinery and enhance transcription best fits this broad role, since activators work by bringing in or facilitating the assembly of the proteins needed to start or boost transcription. Some activators act by directly recruiting RNA polymerase, while others act indirectly by modifying chromatin or bringing in coactivators; the key idea is that binding to DNA leads to greater transcription. The other options describe a repressor that blocks transcription or a molecule that degrades RNA, which do not capture the activator function.