T7 and SP6 RNA polymerases are DNA dependent RNA polymerases that produce DNA templated RNA transcripts. T7 and SP6 exhibit high specificity for their respective promoters. Both T7 and SP6 can be used for the in vitro synthesis of RNA for a wide variety of applications, including transfection, translation, structural studies and radioactive and non-isotopic probe generation. E. coli Poly(A) Polymerase and Poly(U) Polymerase generate untemplated homoribopolymeric tails on RNA 3´-ends. Both E. coli Poly(A) Polymerase and Poly(U) Polymerase can be used for RNA tailing prior to reverse transcription or for direct labeling.