DNA-dependent RNA polymerase catalyzes the transcription of DNA into RNA using the four ribonucleoside triphosphates as substrates. Component of RNA polymerase II which synthesizes mRNA precursors and many functional non-coding RNAs. Pol II is the central component of the basal RNA polymerase II transcription machinery. It is composed of mobile elements that move relative to each other. Component of RNA polymerase IV which mediates short-interfering RNAs (siRNA) accumulation and subsequent RNA-directed DNA methylation-dependent (RdDM) transcriptional gene silencing (TGS) of target sequences. Component of the RNA polymerases II and IV complexes. Interacts with NRPD1. Expressed in roots, leaves and seeds, and to a lower level, in flower buds, flowers and siliques. Belongs to the archaeal Rpo5/eukaryotic RPB5 RNA polymerase subunit family.