Q.62 What is true about bacterial DNA-dependent RNA Polymerase.

A. It is an oligomer of approximately 400KDa.
B. Its beta(ß) subunit together with Mg2T converts ribonucleotides into RNA.
C. a-amanitin strongly inhibits the enzyme.
D. The enzyme can also form DNA from RNA.

Choose the most appropriate answer from the options given below :

1. B and C Only

2. C and D Only

3. A and B Only

4. A, B, and D Only

Bacterial RNA Polymerase Essentials

Bacterial RNA polymerase (core enzyme: α₂ββ’ω) transcribes DNA to RNA, essential for gene expression in microbiology and biochemistry exams. Molecular weight ~400 kDa; Mg²⁺ catalyzes phosphodiester bonds. This MCQ tests structure vs function myths.

Correct Answer: Option 3 (A and B Only)

Core enzyme mass ≈ 400 kDa (α₂ ~70 kDa, β ~150 kDa, β’ ~150 kDa, ω ~10 kDa). β subunit (with Mg²⁺ in active site) polymerizes NTPs to RNA. C false (α-amanitin targets eukaryotic Pol II); D false (reverse transcriptase does that).

Bacterial RNAP Core Enzyme Components Table

Detailed Option Analysis

• Option 1: B and C Only
  Incorrect. B true (β catalytic); C false—rifampicin inhibits bacterial RNAP, not α-amanitin (eukaryotic-specific).

• Option 2: C and D Only
  Incorrect. Both false: α-amanitin weak on bacterial; D describes retroviral RT, not RNAP.

• Option 3: A and B Only
  Correct. A matches ~400 kDa oligomer; B precise—β/Mg²⁺ forms RNA backbone.

• Option 4: A, B, and D Only
  Incorrect. D false—RNAP unidirectional DNA→RNA.

Exam Tip: Inhibitors and Directionality

Distinguish: Bacterial RNAP sensitive to rifampicin; eukaryotic Pol II to α-amanitin. No reverse activity (unlike Taq Pol reverse mode). Link to prior peptide/α-carbon: RNAP synthesizes mRNA for translation.

Practice: Holoenzyme adds σ (~70 kDa, total ~470 kDa)—why not in A? Core enzyme specified.