Mathematical Modeling: Bridging the Gap between Concept and Realization in Synthetic Biology
Figure 5
Design concepts for the RTC three-counter in Friedland et al. [7]. To count three induction events, the RTC three-counter employs a transcriptional cascade that has three nodes. The constitutive promoter drives transcription of T7 RNA polymerase (T7 RNAP), whose gene product binds the T7 promoter, which in turn controls the transcription of T3 RNAP. Similarly the protein of T3 RNAP binds the T3 promoter and ultimately controls the transcription of GFP. All genes are further downregulated and upregulated by cis and trans elements of riboregulators. A cis repressor (cr) interacts with the downstream ribosome binding site (RBS) in such a manner as to prevent translation. The arabinose promoter drives a transactivating, noncoding RNA (taRNA) that binds to cr in trans, thus relieving this inhibition of translation. Due to this design, protein synthesis at each node requires both transcription and translation to independently happen. Thus this cascade is able to count three arabinose pulses by expressing a different protein in response to each pulse (adapted from Friedland et al. [7]).
