Rifampicin acts by binding the beta subunit of bacterial RNA polymerase. At which step of transcription does this inhibition occur?

• A Promoter recognition by sigma factor
• B Rho-dependent termination
• C Elongation of the RNA chain
• D Formation of the first phosphodiester bond during initiation ✓

Explanation

Rifampicin binds the beta subunit of bacterial RNA polymerase near the RNA exit channel and specifically blocks initiation by preventing formation of the first few phosphodiester bonds; it does not affect elongating complexes. This selectivity underlies its use as an antitubercular agent. Promoter recognition involves the sigma factor, elongation proceeds once the enzyme clears the promoter, and Rho-dependent termination uses a helicase that catches up with the polymerase at rut sites.

Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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