T7 RNA Polymerase

The T7 bacteriophage encodes a single-subunit RNA polymerase of 99 kDa that transcribes the phage's genes during its lytic growth in Escherichia coli. The T7 RNA polymerase is structurally similar to DNA polymerases, reverse transcriptases, and RNA-directed RNA polymerases, and these structural similarities define a polymerase superfamily that includes the majority of nucleic acid-synthesizing enzymes. T7 RNA polymerase is structurally unrelated to the more complex, multi-subunit cellular RNA polymerases that have molecular weights of >500 kDa. Its relative structural simplicity has facilitated description of its structure and mechanism to reveal that progression through its transcription reaction is mediated by a concerted series of large conformational changes. The high activity and stringent promoter specificity of T7 RNA polymerase are exploited in technologies for expressing heterologous genes in vivo, and for synthesizing RNAs in vitro.