rpoB

The rpoB gene encodes the β subunit of bacterial RNA polymerase and the homologous plastid-encoded RNA polymerase (PEP). It codes for 1342 amino acids in E. coli, making it the second-largest polypeptide in the bacterial cell. It is targeted by the rifamycin family of antibacterials, such as rifampin. Mutations in rpoB that confer resistance to rifamycins do so by altering the protein's drug-binding residues, thereby reducing affinity for these antibiotics.

Some bacteria contain multiple copies of the 16S rRNA gene, which is commonly used as the molecular marker to study phylogeny. In these cases, the single-copy rpoB gene can be used to study microbial diversity.

An inhibitor of transcription in bacteria, tagetitoxin, also inhibits PEP, showing that the complex found in plants is very similar to the homologous enzyme in bacteria.