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Circular RNA (circRNA) is a covalently closed single-stranded RNA species that does not require capping or a poly(A) tail and exhibits prolonged transgene expression compared to linear mRNA due to altered degradation kinetics. With these favorable characteristics, IVT circRNA is rapidly being developed for therapeutic applications including vaccines, treating genetic disorders, and modulating the immune system. VectorBuilder specializes in custom circRNA production at a variety of scales.

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Proprietary sequence optimization for coding region and IRES

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Experts design and production team for delivering circRNA with high yield, purity, and expression


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Technical Information

circRNA cyclization and translation

VectorBuilder has developed an optimized production platform for the generation of high-yield and high-purity circRNA based on the Group I permuted intron-exon (PIE) self-splicing technology (Figure 1). The generation of circRNA by this mechanism results in minimal impurities and scar sequence. The translation of circRNA is IRES-dependent. The IRES recruits the ribosome to initiate translation internally on a transcript independent of its 5' end.


Figure 1. Mechanism of circRNA self-splicing and generation in vitro. The translation of circRNA is IRES dependent.

Experimental data

Figure 2. circRNA encoding EGFP was transfected into HEK293T cells and exhibited long-term expression compared to traditional mRNA. 

Comparison of different types of IVT RNA
mRNA circRNA saRNA
Structure Linear; usually contains 5’ cap, 5’ UTR, ORF for GOI, 3’ UTR, and poly(A) tail Circular; usually contains IRES and ORF for GOI Linear; usually contains 5’ UTR, ORFs for replicase genes and GOI, 3’ UTR, and poly(A) tail
Cap Requires 5’ Cap for stability and ribosome recruitment No Cap; relies on IRES for ribosome recruitment Requires 5’ Cap for stability and ribosome recruitment
RNA length (nt) 100 ~ 10,000 1000 ~ 5000 7000 ~ 10,000
Stability Low High Low
Can modified nucleotides be added in production? Yes No Yes
Expression level Low Medium High
Expression duration Short Medium Long
Immunogenicity Low Medium High