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 minimal PEP RNA polymerase found in etioplasts (PEP-B) is composed of four subunits: alpha, beta, beta', and beta''. Following differentiation into chloroplasts the PEP-A RNA polymerase in this organism has been shown to be composed of at least 13 subunits, including the PEP-B subunits. When a (nuclear-encoded) sigma factor is associated with the core the holoenzyme is formed, which can initiate transcription (By similarity). A second beta-like protein with a slightly lower molecular weight has been purified with the PEP-A polymerase as identified by mass spectrometry. Belongs to the RNA polymerase beta chain family.