DNA-dependent RNA polymerase catalyzes the transcription of DNA into RNA using the four ribonucleoside triphosphates as substrates. Second largest component of RNA polymerase II which synthesizes mRNA precursors and many functional non-coding RNAs. Proposed to contribute to the polymerase catalytic activity and forms the polymerase active center together with the largest subunit. 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. NRPB2 is part of the core element with the central large cleft, the clamp element that moves to open and close the cleft and the jaws that are thought to grab the incoming DNA template (By similarity). Essential for the completion of the three rounds of mitosis in female megaspores required for the development of mature gametophytes (PubMed:18723889). a ribonucleoside 5'-triphosphate + RNA(n) = diphosphate + RNA(n+1) Component of the RNA polymerase II complex consisting of at least 12 subunits. Defect in seed production due to female gametophyte developmental arrest. The binding of ribonucleoside triphosphate to the RNA polymerase II transcribing complex probably involves a two-step mechanism. The initial binding seems to occur at the entry (E) site and involves a magnesium ion coordinated by three conserved aspartate residues of the two largest RNA Pol II subunits (By similarity). Belongs to the RNA polymerase beta chain family.