Within the promoter, just upstream of the transcriptional start site, sits a short repeat of thymine and adenine dinucleotides. What is this sequence called, and which transcription factor binds it first?
AThe CpG island, bound first by TFIID
BThe TATA box, first bound by RNA polymerase
CThe TATA box, bound first by TFIID
DThe operator sequence, bound first by CAP
Answer & Solution
Correct answer: C. The TATA box, bound first by TFIID
1. Just upstream of the transcriptional start site, within the promoter, is a sequence called the TATA box.
2. The TATA box is a repeat of thymine and adenine dinucleotides.
3. To initiate transcription, the transcription factor TFIID is the first to bind to the TATA box.
4. Binding of TFIID recruits other transcription factors before RNA polymerase can bind and begin transcription.
5. A CpG island is a cytosine and guanine rich sequence involved in epigenetic regulation, not the thymine and adenine repeat described as the TATA box.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 16 "Gene Expression", section The Promoter and the Transcription Machinery_
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