Riboswitch Inducible Gene Expression via Self-Splicing Introns
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Solution Overview
Problem
Current gene expression systems suffer from 'leaky' expression, where some cells are fully induced while others are not, and exhibit cross-talk, making them difficult for simultaneous and differential expression of multiple genes, especially when toxic genes need controlled expression.
Innovation Solution
A two-component inducible expression system using self-splicing introns and aptamers, where the presence of an inducer triggers self-splicing activity to restore the reading frame and drive gene expression, minimizing background expression and providing tight on/off control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional inducible expression systems are used, then gene expression can be induced, but leaky expression occurs where some cells are fully induced while others are not
Solution Approach 1:
The system employs self-splicing introns that automatically remove themselves from the pre-mRNA transcript when the inducer is present, without requiring external enzymatic processing. This self-service mechanism ensures consistent splicing across all cells, eliminating the variability seen in conventional systems where expression control reliability is compromised by heterogeneous induction states.
Solution Approach 2:
The patent replaces the conventional protein-based transcriptional control mechanism with an RNA-based splicing control mechanism. Instead of relying on inducer-dependent transcription factor binding that varies between cells, the system uses inducer-dependent RNA splicing, which provides more uniform and reliable expression control across the cell population, thereby improving both reliability and manufacturing precision.
2Adaptability or versatility
If conventional inducible promoters are used, then gene expression can be controlled, but cross-talk occurs making simultaneous and differential expression of multiple genes difficult
Solution Approach 1:
The patent segments the gene expression control into independent RNA splicing units, each with its own inducer-specific aptamer-intron system. This allows multiple genes to be controlled by different inducers (e.g., theophylline for one gene, tetracycline for another) without cross-talk, as each splicing event is independently regulated by its specific inducer binding to its specific aptamer, thereby enabling simultaneous and differential expression of multiple genes with high reliability.
Solution Approach 2:
The patent introduces RNA aptamers as intermediary elements that specifically bind to small molecule inducers and trigger splicing of associated introns. These aptamer-intron intermediaries provide a highly specific coupling between inducer and target gene, preventing cross-talk between different inducer-gene pairs and enabling reliable multi-gene expression control with enhanced adaptability.
3Reliability
If conventional expression systems are used, then gene expression can be induced, but background expression levels are high making toxic gene control difficult
Solution Approach 1:
The patent applies preliminary anti-action by placing self-splicing introns with inducer-dependent splicing activity into the coding sequence of the target gene. In the absence of the inducer, the introns remain unspliced and prevent translation, effectively blocking toxic gene expression at the translational level. This preliminary block prevents any background expression of toxic genes, while upon inducer addition, the introns are rapidly removed to allow immediate expression when needed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This system achieves tight, inducer-specific expression with minimal leakage, allowing for precise control of gene expression, reducing background levels by up to 99.9% and ensuring no expression in the absence of the inducer.
Implementation Method 1
A riboswitch comprises an aptamer which binds the inducer molecule (ligand). This ligand binding results in a structural change in the mRNA riboswitch
Implementation Method 2
providing a cell with a first and a second polynucleotide expression construct, the first construct comprising a polynucleotide sequence to be transcribed, and wherein the polynucleotide sequence is interrupted by at least two introns which are self-splicing introns
Data Source
Figure 1A~1B
Figure 1C
Figure 2A
AI summary
An intronic, self-splicing riboswitch is configured for enzyme-product specificity by introducing an appropriate aptamer. This then provides a sensing-expression construct, whereby the presence of an enzyme product in the cell triggers self-splicing of the intron sequence to restore the reading frame of the reporter gene and as such to drive expression of the gene product. The sensing construct expresses a protein which marks the cell or permits its growth or survival in or on an otherwise selective media. In this way, introduction or the presence of such product sensing-reporter constructs in cells can be harnessed to provide a multi-parallel rapid screening of cells or libraries for desirable enzyme variants.