# Enhancing Circular RNA Translation Efficiency Through Dual Internal Ribosome Entry Sites

## TL;DR

Researchers improved the translation efficiency of circular RNA by using two IRES elements from the EMCV family, enhancing its potential for drug delivery.

## Contribution

A novel dual-IRES strategy using EMCV-derived IRES elements to boost circRNA translation efficiency is introduced.

## Key findings

- Translation efficiency is significantly improved with dual EMCV-derived IRES elements.
- EMCV IRESs at both 5′ and 3′ ends of the CDS work cooperatively to enhance expression.
- The strategy is compatible with multiple coding sequences.

## Abstract

Circular RNAs are stable mRNA molecules that do not require expensive chemical modifications, but their application is limited by low translational efficiency because they lack a 5′ cap and rely on IRESs for translation. In this study, we designed a dual-IRES strategy to enhance circRNA translation and tested this approach in 293T cells. Our results show that translation efficiency is significantly improved only when both the 5′ and 3′ IRESs are derived from the EMCV family. This suggests that EMCV IRESs possess structural features that allow effective cooperation in a dual-IRES configuration.

Circular RNA (circRNA) has emerged as a promising vector for drug delivery because, unlike linear mRNA, it does not require costly chemical modifications and offers greater stability and sustained expression in cells. Lacking the canonical 5′ cap structure, circRNA relies primarily on internal ribosome entry sites (IRES) to initiate translation, but IRES-mediated initiation is less efficient than cap-dependent translation. To overcome this limitation, we devised a dual-IRES strategy that introduces a second IRES to drive translation of the coding sequence (CDS). By testing several IRES elements known for high translational activity, this study shows that IRESs derived from the EMCV (Encephalomyocarditis virus) family can enhance expression when placed at the 3′ of the CDS, in coordination with the 5′ EMCV-derived IRES. The optimal dual-IRES combinations identified in this study display compatibility with two different coding sequences, offering a useful strategy to enhance circRNA translation.