Circular RNAs (circRNAs) are more stable than linear RNAs because they are resistant to degradation by exonucleases, making them a promising option for RNA-based therapeutics. However, existing methods for synthesizing circRNAs face several challenges, such as low yields for longer circRNAs, relatively low translation efficiency and difficulties in incorporating chemical modifications. To address these issues, Du et al. have developed a method for synthesizing long circRNAs based on trans-splicing circularization. These methods offer high yields and improved translation efficiency, compatible with RNA modifications.

The team first developed an approach named trans-ribozyme-based circularization (TRIC), which uses the ribozyme activity of a specific group I intron from Anabaena, tRNALeu. By maintaining the ribozyme at the leading end of the RNA sequences, TRIC enhances ribozyme folding and circularization efficiency, enabling the synthesis of circRNAs over 8,000 nucleotides long. The team further optimized the TRIC method to minimize the sequence requirements, allowing the production of circRNAs without bacterial sequences. The resulting circRNAs can be efficiently translated in a process known as rolling circle translation, which produces multiple copies of proteins in one translation initiation event.