DNA-dependent RNA polymerase catalyzes the transcription of DNA into RNA using the four ribonucleoside triphosphates as substrates. a ribonucleoside 5'-triphosphate + RNA(n) = diphosphate + RNA(n+1) The RNAP catalytic core consists of 2 alpha, 1 beta, 1 beta' and 1 omega subunit. When a sigma factor is associated with the core the holoenzyme is formed, which can initiate transcription. Belongs to the RNA polymerase beta chain family. Sequence differs from that shown in the region 864-1035. Sequence differs from that shown in the region 864-1035. Sequence differs from that shown in the region 864-1035.