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IRES-dependent second gene expression is significantly lower than cap-dependent first gene expression in a
H Mizuguchi1, Z Xu, A Ishii-Watabe
1Division of Biological Chemistry and Biologicals, National Institute of Health Sciences, Tokyo, Japan. mizuguch@nihs.go.jp
Summary
Internal ribosome entry site (IRES) elements enable coexpression but show variable downstream gene expression. Researchers quantified IRES efficiency, finding it ranges from 6-100% of cap-dependent expression, impacting bicistronic vector design.
Area of Science:
- Molecular Biology
- Gene Expression
- Biotechnology
Background:
- Internal ribosome entry site (IRES) elements facilitate coexpression of multiple genes from a single messenger RNA transcript.
- The relative efficiency of IRES-driven downstream gene expression compared to cap-dependent upstream gene expression is not well-characterized.
Purpose of the Study:
- To characterize the efficiency of IRES-dependent second gene expression relative to cap-dependent first gene expression in bicistronic vectors.
- To evaluate the impact of IRES sequence derived from encephalomyocarditis virus (EMCV) on gene expression levels.
Main Methods:
- Construction of bicistronic vectors utilizing the EMCV IRES.
- Comparison of IRES-dependent second gene expression with cap-dependent first gene expression in various cultured cell lines.
- In vivo analysis of gene expression in mouse liver.
Main Results:
- IRES-dependent second gene expression varied significantly, ranging from 6% to 100% of the first gene's expression, with most cases falling between 20% and 50%.
- In the absence of an IRES element, second gene expression was substantially lower, typically between 0.1% and 0.8% of the first gene's expression.
Conclusions:
- The efficiency of IRES-mediated downstream gene expression is notably lower than upstream cap-dependent expression.
- Careful consideration of gene positioning and the inherent limitations of IRES elements is crucial for effective bicistronic vector design and application.