Transcription In Vitro Using Bacteriophage RNA Polymerases

Synthesis of specific RNA sequences in vitro is simplified because of the availability of bacteriophage RNA polymerases and specially designed DNA vectors. RNA polymerases encoded by SP6, T7, or T3 bacteriophage genomes recognize particular phage promoter sequences of their respective viral genes with a high degree of specificity (1 –3 ). These RNA polymerases also transcribe DNA templates containing their cognate promoters under defined conditions in vitro (4 ,5 ). Standard reaction conditions for transcription in vitro can be adjusted for synthesis of large amounts of RNA or for smaller amounts of labeled RNA probes.