T7 RNA polymerase can perform in vitro transcription of RNA from DNA templates containing T7 promoter using four NTPs as substrates. T7 RNAi Transcription Kit is an optimized version of T7 High Yield RNA Transcription Kit that is designed for transcription of double-stranded RNA. It can be used to transcribe 21 bp siRNA and long-fragment dsRNA. The purified transcripts can be used for RNAi experiments mediated by cationic liposome, calcium phosphate coprecipitation, electroporation, DEAE-Dextran and microinjection. In general, one reaction produces 20 - 80 μg RNA.