mRNA polymerase is a DNA-dependent mRNA polymerase that is used for in vitro mRNA synthesis with strict specificity for its respective double-stranded promoters. Large quantities of RNA can be synthesized from a DNA sequence cloned downstream under the promoters due to the high processivity and transcription frequency of mRNA polymerase. RNA produced using the mRNA polymerase is suitable for many applications in research and biotechnology, including radiolabeled RNA probe preparation, mRNA for in vitro translation and microinjection, RNA structure, processing, and catalysis studies, RNA amplification, and expression control via anti-sense RNA.