T7 RNA polymerase, expressed by Escherichia coli from the T7 bacteriophage RNA polymerase gene, is a highly specific enzyme utilized for in vitro transcription (IVT) of mRNA. This polymerase requires Mg 2+ and selects only DNA templates that contain the T7 promoter sequence, whether single-stranded or double-stranded. It employs NTPs to synthesize RNA that is complementary to the single-stranded DNA following the promoter [1] [2].