Fig. 1

The design and mechanism of SWT. (A) A SWT consists of two main domains: a linear toehold region and a rho-independent terminator, which in turn encompasses a hairpin stem with a small loop, and a poly U-tract. Fluorescent aptamer 3WJdB is used as the reporter to characterize the transcription efficiency through the change of fluorescence output. A trigger RNA consists of sequences complementary to the stem and toehold regions (denoted by asterisks (*)). The hybridization of trigger RNA and SWT can disrupt the stable hairpin structure of rho-independent terminator to allow transcription of downstream gene. (B) In the absence of the trigger RNA, the terminator structure in SWT halts the transcription process (OFF). In the presence of the trigger RNA, the trigger RNA can initiate hybridization through the toehold region of SWT, and continue the branch migration to disrupt the formation of terminator stem, thereby allowing for the transcription of the downstream reporter (ON)