RNA polymerase is an enzyme that produces RNA and catalyzes the initiation and elongation of RNA chains from a DNA template. RNA is created using a process known as transcription. The RNA polymerase is a key component to this process. The reaction that this enzyme catalyzes for is: (RNA)n + Ribonucleoside Triphosphate ->/<- (RNA)n+1 +PPi. RNA polymerases are relatively large. The size of RNA polymerase in a typical eukaryotic cell is roughly 500kDa.