Rna Pol enzyme fro Promega. Please give me an idea regarding this. The 3 commercial kits available from Ambion, Epicentre and Promega come closest. All 3 use proprietary enzyme mixtures that probably consist of lots of T7 RNAP, an RNase inhibitor enzyme, and yeast inorganic pyrophosphatase. Transcription generates pyrophosphate as a byproduct along with abortive initiation products, and these inhibit transcription.
Yields depend on the size of the template.
T7 RNAP unit definitions also depend on the size of the template and vary among the suppliers. Ambion uses a 300 bp linearized DNA fragment as a transcription template because it allows the measurement of the rate limiting initiation step. Some companies may measure units using 3000 bp supercoiled plasmid templates. Units determined in this manner appear to be higher than units determined on short templates because they are based on the elongation rate which is significantly faster than the initiation rate. Shorter templates require more enzyme activity than longer templates to produce one unit of enzyme activity.