Tailored synthetic sRNAs dynamically tune multilayer genetic circuits

Predictable and controllable tuning of genetic circuits to regulate gene expression, including modulation of existing circuits or constructs without the need for redesign or rebuilding, is a persistent challenge in synthetic biology. Here, we propose a rational design of de novo small RNAs (sRNAs) to dynamically modulate gene expression within a broad range, from high, medium to low repression, and implemented them in Escherichia coli. We designed multiple multilayer genetic circuits, in which the variable effector element is a transcription factor (TF) controlling downstream the production of a reporter protein. Our approach harnesses the intrinsic RNA-interference pathway in E. coli to exert dynamic and modular control of the multilayer genetic circuits. The sRNAs were designed to target TFs instead of the reporter gene, which allowed for wide range of expression modulation of the reporter protein, including the most difficult to achieve dynamic switch to an OFF state. Out work provides a frame for achieving independent modulation of gene expression, by only including an independent control circuit expressing synthetic sRNAs, without altering the structure of existing genetic circuits.