Split Reporters Facilitate Monitoring of Gene Expression and Peptide Production in Linear Cell-Free Transcription–Translation Systems

Cell-free transcription-translation (TXTL) systems expressing genes from linear dsDNA enable rapid prototyping of genetic devices while avoiding cloning steps. However, repetitive inclusion of a reporter gene is an incompressible cost and sometimes accounts for most of the synthesized DNA length. Here we present minireporters based on split-GFP systems that reassemble into functional fluorescent proteins and can be used to monitor gene expression in E. coli TXTL. The 135 bp GFP10-11 fragment produces a fluorescent signal comparable to its full-length GFP counterpart when reassembling with its complementary protein synthesized from the 535 bp fragment expressed in TXTL. We show that minireporters can be used to characterize promoter libraries, with data qualitatively comparable to full-length GFP, and matching with in vivo expression measurements. We also use minireporters as small fusion tags to measure TXTL protein and peptide production yield. Finally, we generalize our concept by providing a luminescent minireporter based on split-nanoluciferase. The ~80% gene sequence length reduction afforded by minireporters lowers synthesis costs and liberates space for testing larger devices while producing a reliable output. In the peptide production context, the small size of minireporters compared to full-length GFP is less likely to bias peptide solubility assays. We anticipate that minireporters will facilitate rapid and cost-efficient genetic device prototyping, protein production, and interaction assays.