Rifampicin is associated with which mechanism of action?

Rifampicin primarily acts by inhibiting RNA synthesis, which is achieved through its interaction with DNA-dependent RNA polymerase. This enzyme is crucial for transcription, the process of synthesizing RNA from a DNA template. By binding to the β-subunit of the RNA polymerase, rifampicin prevents the formation of the transcription complex, effectively halting the synthesis of mRNA and, consequently, bacterial proteins. This mechanism is particularly significant in the treatment of bacterial infections, such as tuberculosis, where ribosomal RNA and messenger RNA synthesis plays a vital role in the growth and replication of bacteria.

In contrast, other mechanisms listed in the question involve different targets. Inhibition of DNA synthesis would target the processes or enzymes involved in DNA replication rather than RNA synthesis. Inhibition of protein synthesis would interfere with the ribosomal machinery but does not involve the transcription of RNA itself. Lastly, inhibition of cell wall synthesis is a characteristic mechanism of action for antibiotics like penicillins and cephalosporins, which target the bacterial cell wall rather than the transcription process. Thus, the action of rifampicin is specifically related to inhibiting RNA synthesis, making this the correct answer.