Q.62 Transcription factors that mediate the binding of RNA polymerase to DNA template are
(A).TFIIA
(B).TATA box
(C).TFIIB
(D).Small nuclear ribonucleoproteins
1. (A) and (D).
2. (A) and (C) .
3. (C) and (D).
4. (B) and (D).
Title: Transcription Factors Binding RNA Polymerase to DNA: TFIIA & TFIIB Explained (MCQ Solved)**
TFIIA and TFIIB are general transcription factors (GTFs) that mediate RNA polymerase II binding to promoter DNA during eukaryotic transcription initiation.
Correct Answer: 2. (A) and (C)
In the basal transcription apparatus, TFIIA stabilizes TBP (TATA-binding protein) binding to the TATA box, while TFIIB bridges TBP-DNA complex to Pol II, positioning it precisely at the transcription start site for pre-initiation complex (PIC) assembly. Both are essential GTFs in the ordered recruitment: TFIIA/TFIIB → TFIID → TFIIF/Pol II → TFIIE/H.
PIC Assembly Sequence
-
TFIID (TBP+TAFs) recognizes TATA/promoter.
-
TFIIA stabilizes TBP-DNA interaction.
-
TFIIB recruits Pol II-TFIIF complex.
-
TFIIE/H complete PIC for promoter melting/initiation.
Explanation of All Options
| Option | Type | Role in Transcription |
|---|---|---|
| (A) TFIIA | GTF protein | Stabilizes TBP at promoter; essential for Pol II recruitment. |
| (B) TATA box | DNA sequence | Promoter element (~25 bp upstream TSS); not a protein factor. |
| (C) TFIIB | GTF protein | Bridges promoter to Pol II; recognizes BRE elements. |
| (D) snRNPs | RNA-protein complexes | Splicing machinery (spliceosome); act post-transcriptionally. |
| Choice | Combination | Correct? |
|---|---|---|
| 1. (A) and (D) | TFIIA + snRNPs | No: snRNPs unrelated to initiation. |
| 2. (A) and (C) | TFIIA + TFIIB | Yes: Core GTFs for Pol II-DNA binding. |
| 3. (C) and (D) | TFIIB + snRNPs | No: snRNPs process pre-mRNA. |
| 4. (B) and (D) | TATA + snRNPs | No: TATA is DNA; snRNPs post-transcriptional. |
