Binds to RNA polymerase (RNAP), probably stimulating transcriptions from principal, but not alternative sigma factor promoters (By similarity). Partially restores transcription in the presence of rifampicin (Rif) in vitro; overexpression leads to an increase in the Rif tolerance in vivo, with smaller colonies. Seems to act by removing Rif from its binding site and preventing its further binding. No longer stimulates transcription in Rif-resistant RNA polymerase (with mutations in rpoB). Monomer. Forms a complex with the RNAP catalytic core, specifically with the beta subunit (RpoB); its binding site may overlap with that of Rif. May bind free principal sigma factors. Constitutively expressed during growth, increases slightly in stationary phase (at protein level). Belongs to the RNA polymerase-binding protein RbpA family. Extended N-terminus.