Eukaryotic transcription initiation: Which general transcription factor complex binds first at the TATA box?

Introduction / Context:Accurate transcription by RNA polymerase II requires assembly of general transcription factors at promoters. At many TATA-containing promoters, a characteristic order of assembly begins with TFIID recognizing the TATA box.

Given Data / Assumptions:

• Promoter contains a TATA element.
• General transcription factors include TFIID (TBP + TAFs), TFIIA, TFIIB, and others.
• The question asks which factor binds first.

Concept / Approach:TFIID contains TBP (TATA-binding protein), which bends DNA on binding the TATA sequence, serving as a platform for subsequent factors (TFIIA, TFIIB) and recruitment of RNA polymerase II with TFIIF, followed by TFIIE and TFIIH.

Step-by-Step Solution:

Verification / Alternative check:In vitro reconstitution shows TBP/TFIID binding is the earliest and required step for many TATA promoters.

Why Other Options Are Wrong:

• TFIIA and TFIIB bind after TFIID to stabilize the complex and help Pol II positioning.
• “All of these” misstates the ordered assembly pathway.

Common Pitfalls:Assuming all promoters assemble identically; TATA-less promoters can recruit via other core elements, but TBP/TFIID is still central.

Final Answer:Transcription factor IID (TFIID with TBP)