In gene regulation, what is the primary function of transcription factors in eukaryotes?

• A. They are enzymes that synthesize RNA.
• B. They bind to DNA to promote or repress transcription, often needing enhancers and RNA polymerase II.
• C. They catalyze DNA replication.
• D. They degrade mRNA after transcription.

Answer: (B)

Transcription factors regulate gene expression by binding to specific DNA sequences and helping to control transcription initiation. In eukaryotes, turning a gene on typically requires more than RNA polymerase II; transcription factors recruit the general transcription machinery and often interact with activators bound at enhancers, which can act from a distance through DNA looping. Activator factors promote the assembly of the preinitiation complex and recruitment of RNA polymerase II, boosting transcription, while repressor factors can block this assembly or recruit enzymes that modify chromatin to suppress transcription. This binding-and-recruitment role is why transcription factors are described as binding DNA to promote or repress transcription, with enhancers and RNA polymerase II frequently involved. They are not enzymes that synthesize RNA, they do not catalyze DNA replication, and they do not degrade mRNA.