18. Genetic studies demonstrated that TBP mutant cell extracts are deficient in transcription of genes from all three promoters viz. class I, II and III. Following statements describe characteristic features of TBP.
(A) TBP is considered as an universal basal transcription factor.
(B) TBP is not required for transcription of archaeal genes.
(C) TBP is involved in recognizing TATA box.
(D) TBP operates at all promoters regardless of their TATA content.
Which of the following combinations is NOT correct?
(1) A and D   (2) C and D
(3) B and D   (4) A and C

The correct answer is (3) B and D.

Detailed Explanation

Let’s assess each statement about TBP (TATA-binding protein):

A. TBP is considered as a universal basal transcription factor.
Correct.
TBP is indeed a universal transcription factor required for initiation by all three nuclear RNA polymerases (I, II, and III) in eukaryotes. It is essential for transcription of almost all nuclear genes.

B. TBP is not required for transcription of archaeal genes.
Incorrect.
TBP is required for transcription in both eukaryotes and archaea. In archaea, TBP is a central component of the transcription machinery, similar to its role in eukaryotes.

C. TBP is involved in recognizing TATA box.
Correct.
TBP binds specifically to the TATA box sequence in gene promoters, distorting the DNA and facilitating the assembly of the transcription preinitiation complex.

D. TBP operates at all promoters regardless of their TATA content.
Incorrect.
While TBP is required for transcription from both TATA-containing and TATA-less promoters, its mode of action can differ. For TATA-less promoters, TBP is recruited via other proteins and does not directly recognize a TATA box. Thus, saying TBP “operates at all promoters regardless of their TATA content” is an oversimplification; its direct DNA binding is specific to TATA boxes, while indirect recruitment occurs at TATA-less promoters.

Therefore, B and D are NOT correct.

Summary Table

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