 In biotechnology applications, T7 RNA polymerase is commonly used to transcribe DNA that has been cloned into vectors that have two (different) phage promoters (e.g., T7 and T3, or T7 and SP6) in opposite orientation.RNA can be selectively synthesized from either strand of the insert DNA with the different polymerases.The enzyme is stimulated by spermidine and "in vitro" activity is increased by the presence of carrier proteins (such as BSA)

Homogeneously labeled single-stranded RNA can be generated with this system.