Abstract
Background: Programmed ribosomal frameshifting (PRF) is a translational mechanism that enables the ribosome to shift reading frames and access alternative coding sequences. PRF occurs naturally in a wide range of organisms, including viruses, bacteria, and eukaryotes, where it supports compact encoding and stoichiometric control of protein expression. Despite the great potential of PRF in synthetic circuit designs, a broader adoption of PRF in circuit designs has been hampered by rather strict sequence constraints and structural requirements. Results: This work introduces a synthetic translational regulatory platform, protein-inducible ribosomal frameshifting (PIRF), by integrating aptamer-protein interactions with a - 1 PRF motif to enable regulated translation in Escherichia coli. PIRF modules respond to intracellular RNA-binding proteins such as PP7 and MS2, triggering frameshifting in a condition-dependent manner. PIRF could be used to program logic gate operations through frame-dependent translation and enable multilayered regulation in synthetic circuits. Further, the flexible PIRF designs enable reading frame-dependent control of fusion protein expression, protein aggregation, and periplasmic localization via strategic positioning of peptide tags and protein coding sequences. While PIRF enabled regulated frameshifting and could be flexibly reconfigured for a variety of circuits and applications, a measurable level of basal frameshifting was often observed, which may require additional strategies for further optimization in the future. Together, PIRF supports applications in programmable and logical control of downstream protein expression, including condition-dependent aggregation and regulated subcellular localization. Conclusions: PIRF provides a compact and genetically encoded strategy for programmable protein-level regulation, expanding the synthetic biology toolkit for translational control, biosensing and biotherapeutics.