Recombinant tagging system using ribosomal frameshifting to monitor protein expression

Introducing a class of standardized and interchangeable parts utilizing programmed ribosomal frameshifts for synthetic biology applications

Synthetic biology and the rational design of biological devices depend on the availability of standardized and interchangeable biological parts with diverse range of functions. Reliable access to different reading frames during translation has largely been overlooked as functionality for bioengineering applications. Here we report the construction and initial characterization of the first member of such a class of biological parts that conforms to the BioBrick Standard (RFC25), allowing its interchangeable use in biological devices. Using our standardized frameshifting signal consisting of a UUUAAAG slippery sequence, a 6 nt spacer and an engineered pseudoknot based on the infectious bronchitis virus pseudoknot PK401 embedded in a dual reporter construct, we confirm that the frameshifting activity is comparable to the previously published frequency despite the introduced sequence changes. The frameshifting activity is demonstrated using SDS-PAGE and fluorescence spectroscopy. Standardized programmable ribosomal frameshift parts with specific frameshifting frequencies will be of utility for applications such as double coding DNA sequences by expanding the codable space into the -1 frame. Programmed shifting into the -1 frame to bypass a stop codon allows labeling of a protein pool with a fixed stoichiometry of fusion protein, as well as the construction of multi-enzyme expression constructs with specific expression ratios. A detailed understanding of the structural basis of programmed frameshifting will provide the opportunities to rationally design frameshifting elements with a wide range of applications in synthetic biology, including signals that are regulated by small ligands.