Tuning the dynamic range of bacterial promoters regulated by ligand-inducible transcription factors

TLDR

Synthetic biologists struggle to predictably tune ligand‑inducible promoters because controlling the dynamic range—the absolute difference between ON and OFF states—is challenging. The study presents a method to adjust the dynamic range of ligand‑inducible promoters for desired ON/OFF behavior. The authors constructed combinatorial AraC‑ and LasR‑regulated promoters with varied −10/−35 sites, selecting four sequences to assemble multi‑input logic gates controlled by two or three ligand‑inducible transcription factors. The method allows predictable tuning of promoter dynamic range, enabling reliable control of regulatory components.

Abstract

Abstract One challenge for synthetic biologists is the predictable tuning of genetic circuit regulatory components to elicit desired outputs. Gene expression driven by ligand-inducible transcription factor systems must exhibit the correct ON and OFF characteristics: appropriate activation and leakiness in the presence and absence of inducer, respectively. However, the dynamic range of a promoter (i.e., absolute difference between ON and OFF states) is difficult to control. We report a method that tunes the dynamic range of ligand-inducible promoters to achieve desired ON and OFF characteristics. We build combinatorial sets of AraC-and LasR-regulated promoters containing −10 and −35 sites from synthetic and Escherichia coli promoters. Four sequence combinations with diverse dynamic ranges were chosen to build multi-input transcriptional logic gates regulated by two and three ligand-inducible transcription factors (LacI, TetR, AraC, XylS, RhlR, LasR, and LuxR). This work enables predictable control over the dynamic range of regulatory components.