In vitro transcription (IVT) is an elegant way to obtain highly pure and uniform mRNA oligonucleotides of lengths ranging from about 15 to several thousand nucleotides. It is transcribed from a double-stranded DNA template by RNA polymerase (T7, T3 or SP6 RNA polymerase).https://mrna.creative-biolabs.com/category-in-vitro-transcription-vector-452.htm
