A synthetic biology approach to bacterial transcription initiation: RNA aptamer based in vitro transcription assay for rapidly testing bacterial RNA polymerases, promoters and inhibitors.

We present a robust and versatile in vitro transcription (IVT) assay based on an optimized Broccoli RNA aptamer sequence. When paired with the fluorophore DFHBI-1T, this system enables real-time monitoring of multi-round transcription over several hours. To facilitate streamlined promoter analysis, we developed the pIVT3 plasmid backbone. The system was validated using both the single-subunit T7 RNA polymerase and the multi-subunit Escherichia coli RNA polymerase; notably, the activity of the E. coli enzyme remained strictly dependent on the presence of a {sigma} factor and a cognate promoter. To optimize the signal-to-noise ratio, we incorporated two rrnBT1 terminators upstream of the promoter of interest. This modification effectively eliminated background transcription for weak promoters (PlivJ) and prevented interference from read-through transcription in strong synthetic promoters (Ptrc*). Furthermore, we demonstrated the assays utility for drug discovery by characterizing the time- and dose-dependent inhibitory kinetics of rifampicin. Collectively, these results establish the Broccoli-based IVT system as a highly adaptable platform for quantifying promoter strength and screening small-molecule inhibitors of bacterial transcription. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=141 SRC="FIGDIR/small/744185v1_ufig1.gif" ALT="Figure 1"> View larger version (42K): org.highwire.dtl.DTLVardef@1e0c991org.highwire.dtl.DTLVardef@d154aeorg.highwire.dtl.DTLVardef@10e95fcorg.highwire.dtl.DTLVardef@98ea80_HPS_FORMAT_FIGEXP M_FIG C_FIG