Synthetic intervening sequence intron
Synthetic intron element from the pIRES-neo bicistronic expression vector used as a baseline control for intron comparison studies. Shows moderate expression enhancement and serves as a reference point for evaluating other intron elements in mammalian cell expression systems.
Origin: Synthetic (designed for pIRES vector system)
Characteristics
Synthetic intron sequence designed for inclusion in bicistronic expression vectors utilizing internal ribosome entry sites (IRES). Functions as a moderate expression enhancer in mammalian cells when positioned downstream of the CMV promoter. In comparative studies by Xu et al. (2018), IVS intron served as the baseline (1.0-fold) reference, showing lower performance than SV40 intron (4.39-fold) and hCMV intron A (3.69-fold) but higher activity than TPL intron (0.18-fold) and CHEF1 intron (0.008-fold) in stable CHO cell transfections. Maintains consistent expression across cell types without introducing significant variability in transgene expression levels.
Applications: Standard control element in pIRES-neo and related bicistronic expression vectors for mammalian cell transfection experiments. Suitable for applications requiring moderate, predictable transgene expression without extreme enhancement. Commonly used as a reference intron in comparative studies evaluating novel or optimized intron elements for expression vector design. Compatible with both transient and stable transfection systems in CHO, HEK293, and other mammalian cell lines.
Limitations: Moderate expression enhancement is significantly lower than optimized intron elements like SV40 intron (4.4× less) or hCMV intron A (3.7× less) in stable CHO cell lines. Performance may vary depending on promoter context and cell type. As a synthetic element, lacks the evolutionary optimization present in naturally occurring viral introns. Not recommended for applications requiring maximum transgene expression or when cargo space constraints necessitate smaller elements.
Mechanism: Functions through standard splicing-mediated enhancement mechanisms common to introns. Upon transcription, the IVS intron sequence is recognized and excised by the cellular spliceosome, resulting in deposition of the exon junction complex (EJC) upstream of the splice junction. This EJC enhances nuclear mRNA export, increases transcript stability, and improves translation efficiency during the pioneer round of translation. The moderate enhancement levels suggest less efficient EJC recruitment or mRNA processing compared to highly optimized viral intron elements.
Sequence
References
- Xu et al. (2018). SV40 intron, a potent strong intron element that effectively increases transgene expression in transfected Chinese hamster ovary cells. J. Cell. Mol. Med. - Xu 2018 Intron Comparison