An Assay Method for Characterizing Bacteriophage T7 RNA Polymerase Activity by Transcription–Translation (TX-TL) System

T7 system is a commonly used in protein expression and the highest transcription activity of T7 RNAP usually caused the instability of T7 system. In order to apply T7 system extensively, it is essential to characterize T7 RNAP activity. In the present paper, an assay method for T7 RNAP activity was developed with a transcription–translation (TX-TL) system. After the optimization of TX-TL system, the operating parameters were determined as 34°C, 60 min with 20 ng/μl of plasmid DNA template. The standard curve of TX-TL assay method indicated an excellent correlation (r = 0.998), and the sensitivity was better than that of western blotting method. The precision investigation indicated a mean-relative error of 2.58% and a standard-relative error of 7.01%. Moreover, the cell lysate could be added directly to the optimized TX-TL system without affecting T7 RNAP activity assay. The feasibility of present method was further confirmed by characterizing T7 RNAP activity in cell lysate of five strains of Escherichia coli (E. coli) DH5α with different T7 RNAP activities and seven commercial strains of E. coli (DE3). The present assay method for T7 RNAP activity would have a great application in synthetic biology, metabolic engineering, enzyme engineering and biomedicine.