DNA-dependent RNA polymerase (RNAP) catalyzes the transcription of DNA into RNA using the four ribonucleoside triphosphates as substrates (Probable). This subunit is involved in DNA promoter recognition (PubMed:22848102). a ribonucleoside 5'-triphosphate + RNA(n) = diphosphate + RNA(n+1) Binds at least 1 Zn(2+) ion per subunit. Part of the 13-subunit RNA polymerase complex. Belongs to the RNA polymerase beta chain family.