Where do many eukaryotic transcription factors bind to regulate gene expression?

• A. Proximal promoters only
• B. Distal elements such as enhancers
• C. rRNA genes
• D. Origins of replication

Answer: (B)

Distal regulatory elements called enhancers are the primary sites where many eukaryotic transcription factors bind to control gene expression. Enhancers can be located far away from the gene they regulate—upstream, downstream, or within introns—and they don’t have to be in a fixed orientation. When transcription factors bind these sites, they recruit coactivators and the Mediator complex and promote DNA looping so the enhancer-bound factors can interact with the promoter-bound transcription machinery. This setup boosts or modulates RNA polymerase II recruitment and activity, enabling precise, tissue-specific, and condition-dependent control of transcription.

Nearby promoter regions also bind transcription factors, but many important regulatory inputs come from enhancers, which explains why distal elements are emphasized. rRNA genes are regulated by factors specific to RNA polymerase I and are not the typical targets of the general transcription factors that regulate most protein-coding genes. Origins of replication are unrelated to transcription factor binding and regulate DNA replication instead.