13. Which one of the following statements is NOT a correct feature of Escherichia coli RNA polymerase?
(1) Presence of the σ subunit along with α2ββ’ω core RNA polymerase is required for its promoter specific binding.
(2) Presence of the σ subunit along with α2ββ’ω core RNA polymerase is not necessary for the core RNA polymerase  α2ββ’ω to bind to the DNA template.
(3) Mutations in β subunit in its rifampicin resistance defining region (RRDR) confer rifampicin resistance phenotype.
(4) Mutations in σ subunit in its rifampicin resistance defining region (RRDR) confer rifampicin resistance phenotype.

Correct Answer: (4)

“Mutations in σ subunit in its rifampicin resistance defining region (RRDR) confer rifampicin resistance phenotype.”

This statement is NOT correct, making it the right choice for the MCQ.

Detailed Explanation

Let’s analyze each statement:

(1) Presence of the σ subunit along with α₂ββ′ω core RNA polymerase is required for its promoter-specific binding.

• True

• The σ subunit is essential for the RNA polymerase to recognize and bind to specific promoter sequences.

• Without σ, the core enzyme binds DNA non-specifically.

(2) Presence of the σ subunit along with α₂ββ′ω core RNA polymerase is not necessary for the core RNA polymerase to bind to the DNA template.

• True

• The core enzyme (α₂ββ′ω) can bind DNA, but not promoter-specifically.

• Hence, σ is needed for specific initiation, but not for general DNA binding.

(3) Mutations in β subunit in its rifampicin resistance defining region (RRDR) confer rifampicin resistance phenotype.

• True

• Rifampicin, an antibiotic, targets the β subunit of RNA polymerase.

• Mutations in the RRDR region of the β subunit (rpoB gene) lead to rifampicin resistance.

(4) Mutations in σ subunit in its rifampicin resistance defining region (RRDR) confer rifampicin resistance phenotype.

• False / NOT correct

• The σ subunit is NOT the target of rifampicin.

• The drug binds near the RNA exit tunnel of the β subunit.

• There is no RRDR region in the σ subunit.

Conclusion

Only statement (4) is incorrect, making it the correct answer for this question.