Eukaryotic gene transcription depends on RNA polymerase and regulatory proteins working together. Unlike prokaryotic RNA polymerase, eukaryotic RNA polymerase cannot initiate transcription on its own. This lesson explains how promoter sequences and transcription factors assemble the transcription machinery, how enhancers increase transcription, and how repressors can reduce or prevent it.
All flashcards
What is the role of a promoter?
A promoter is a DNA region immediately upstream of a gene that provides binding sites for transcription factors and helps control the initiation of transcription.
What does TFIID do at a TATA box?
TFIID, which contains the TATA-binding protein, binds the TATA box and helps recruit other general transcription factors and the transcription machinery to the promoter.
How do promoter-proximal elements regulate transcription?
Sequences such as CAAT and GC boxes bind specific transcription factors near the core promoter. Those factors interact with the promoter machinery to enhance or repress transcription.
How can an enhancer regulate a distant gene?
An activator binds the enhancer, and DNA bending or looping brings the enhancer-bound protein into contact with proteins at the promoter, helping regulate transcription initiation.
How do transcriptional repressors turn genes down or off?
Repressors bind promoter or enhancer regions and interfere with activating factors or the transcription machinery, reducing or preventing transcription.
Quiz questions
Why can eukaryotic RNA polymerase not initiate transcription by itself?Answer: General transcription factors help assemble the initiation complex, which RNA polymerase cannot form alone.
What is the TATA box, and where is it commonly found?Answer: A core-promoter motif, usually 5′-TATAAA-3′, about 25–35 bases upstream of the transcription start site.
Which statement correctly distinguishes general from specific transcription factors?Answer: General factors help assemble machinery at core promoters; specific factors bind regulatory sites and modify transcription.
A regulatory DNA sequence thousands of nucleotides from a promoter increases transcription when an activator binds it. How can it act on the promoter?Answer: DNA can bend or loop, bringing the enhancer-bound activator near promoter-bound factors and RNA polymerase.
A signal causes a repressor to bind a promoter region and prevent an activator from helping the transcription machinery. What is the likely result?Answer: Transcription of the regulated gene decreases or is blocked.
Based on Biology 2e by Mary Ann Clark, Matthew Douglas, Jung Choi (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.