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) RNAP is composed of a core of 2 alpha, a beta and a beta' subunit. The core is associated with a delta subunit, and at least one of epsilon or omega (PubMed:6802805, PubMed:18289874, PubMed:21710567). When a sigma factor is associated with the core the holoenzyme is formed, which can initiate transcription (PubMed:18289874). Belongs to the RNA polymerase beta chain family.