Multifunctional Systems in Synthetic Biology: Single-Stranded DNA Signaling for Precise Control of Gene Activation

ABSTRACT Controllable gene circuits that respond to defined inputs are essential tools in synthetic biology. By leveraging regulatory mechanisms at either transcriptional or translational levels, synthetic responsive systems have been engineered to recognize diverse signals, such as small molecules (e.g., tetracycline) or physical stimuli (e.g., light). However, these approaches have limitations: small-molecule signals often require high concentrations to be effective, and sophisticated engineering is needed to generate responsive effectors. Here, we establish a simple, versatile gene activation system in which short single-stranded DNAs trigger RNA or protein production by complementing defective single-stranded promoters upstream of target genes. We demonstrate selective gene activation with orthogonal promoters, and logic-gate operations with signal pairs. The signaling system operates in compartmentalized nanoliter droplets scaffolded by bilayers. Signal delivery is controlled by selectively disrupting bilayers or applying transmembrane potential to move signals through protein pores, thereby activating genes within the receiver compartments. This work expands the toolset for engineering multifunctional, responsive materials to meet biotechnological and medical needs, enabling gene activation in response to specific cues.