High Quality Content by WIKIPEDIA articles! RNA polymerase II (also called RNAP II and Pol II) is an enzyme found in eukaryotic cells. It catalyzes the transcription of DNA to synthesize precursors of mRNA and most snRNA and microRNA. A 550 kDa complex of 12 subunits, RNAP II is the most studied type of RNA polymerase. A wide range of transcription factors are required for it to bind to its promoters and begin transcription. In the process of transcription (by any polymerase) there are three main stages: 1. Initiation; the construction of the RNA polymerase complex on the gene's promoter with the help of transcription factors. 2. Elongation; the actual transcription of the majority of the gene into a corresponding RNA sequence, highly moderated by several methods. 3. Termination; the cessation of RNA transcription and the disassembly of the RNA polymerase complex.