Which of the following is an example of a drug that inhibits nucleic acid synthesis?

Rifampin is a drug that inhibits nucleic acid synthesis by targeting bacterial RNA polymerase, which plays a crucial role in the transcription process of converting DNA into RNA. By binding to RNA polymerase, Rifampin prevents the enzyme from synthesizing RNA, thereby stopping the production of essential proteins needed for bacterial growth and replication. This mechanism makes Rifampin particularly effective against certain types of bacteria, including those that cause tuberculosis.

In contrast, the other drugs mentioned operate through different mechanisms. Gentamicin is an aminoglycoside antibiotic that primarily inhibits protein synthesis by binding to the 30S ribosomal subunit. Polymyxin disrupts bacterial cell membrane integrity, leading to cell death but does not directly affect nucleic acid synthesis. Tetracycline also inhibits protein synthesis, but it does so by binding to the 30S ribosomal subunit, preventing the attachment of aminoacyl-tRNA. Therefore, among the choices provided, Rifampin is specifically known for its role in inhibiting nucleic acid synthesis.