19. Which one of the following statements about TATA Binding Protein (TBP) is NOT true?
(1) It is a component of transcription factor TFIID.
(2) TBP recognizes the TATA element by inserting one of its α-helices into the major groove of DNA.
(3) The TBP-DNA interaction causes the DNA to bend.
(4) The TBP-DNA interaction is governed in part by the intercalation of the side chains of phenylalanine residues of TBP between the base pairs at the two ends of the TATA element sequence.
The correct answer is (2) TBP recognizes the TATA element by inserting one of its α-helices into the major groove of DNA.
Detailed Explanation of TBP and Its DNA Interaction
TATA Binding Protein (TBP) is a key component of the general transcription factor TFIID and plays a crucial role in initiating transcription by RNA polymerase II. Here are the facts about TBP relevant to the options:
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TBP is a component of TFIID
This is true. TBP forms the core of TFIID and is responsible for recognizing promoter DNA. -
TBP binds the TATA box by inserting into the DNA minor groove, not the major groove
This statement is false and the correct answer. Unlike many DNA-binding proteins that insert α-helices into the major groove, TBP binds the minor groove of the TATA box DNA. It uses a saddle-shaped structure with a β-sheet surface that wedges into the minor groove, bending the DNA sharply (~80–90°). -
TBP-DNA interaction causes DNA bending
This is true. TBP binding introduces a sharp bend in the DNA, which helps in melting the DNA strands and assembling the transcription preinitiation complex -
TBP-DNA interaction involves intercalation of phenylalanine side chains
This is true. Phenylalanine residues from TBP insert between base pairs at the ends of the TATA element, stabilizing the DNA bend and partially unwinding the helix.
Summary Table
| Statement | True/False | Explanation |
|---|---|---|
| (1) TBP is a component of TFIID | True | TBP is the DNA-binding subunit of TFIID |
| (2) TBP inserts α-helix into major groove | False | TBP binds the minor groove via a β-sheet saddle |
| (3) TBP-DNA interaction bends DNA | True | TBP bends DNA by ~80–90° to facilitate transcription |
| (4) Phenylalanine residues intercalate DNA | True | Phenylalanines intercalate at TATA box ends to stabilize binding |
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