A Synthetic Riboswitch to Regulate Haloarchaeal Gene Expression

Area of Science:

• Synthetic biology
• Microbial genetics
• Molecular biology

Background:

• Synthetic translational riboswitches are crucial for genetic circuits in bacteria, modulating gene expression via the Shine-Dalgarno (SD) sequence.
• Haloarchaeal translation does not strictly require an SD sequence, and high intracellular salt concentrations limit synthetic riboswitch applications.
• Existing synthetic riboswitches often mask both the SD sequence and the start codon.

Purpose of the Study:

• To engineer and apply synthetic theophylline-dependent translational riboswitches in the haloarchaeon *Haloferax volcanii*.
• To investigate the impact of environmental factors like salt concentration and temperature on riboswitch performance.
• To construct a genetic circuit using a riboswitch to control gene expression.

Main Methods:

• Theophylline-dependent translational riboswitches (variants A-E and E*) were introduced into *Haloferax volcanii*.
• Riboswitch function was assessed by measuring reporter gene (*bgaH*) expression in response to theophylline.
• The effects of varying NaCl concentrations (3-4 M) and temperatures (45°C to 30°C) on riboswitch activity were evaluated.
• Riboswitch E was integrated into a genetic circuit to regulate a transcriptional activator (GvpE) controlling a *mgfp6* reporter gene.

Main Results:

• Riboswitch E demonstrated dose-dependent activation of the *bgaH* reporter gene, up to threefold.
• Increased salt concentration (4 M NaCl) enhanced riboswitch E's switching capacity by 12-fold.
• Reduced cultivation temperature (30°C) increased riboswitch E's switching activity up to 26-fold.
• A genetic circuit utilizing riboswitch E successfully regulated reporter gene expression in a dose-dependent manner.

Conclusions:

• Synthetic theophylline-dependent translational riboswitches can be effectively applied in haloarchaea like *Haloferax volcanii*.
• Environmental conditions, specifically high salt and low temperature, significantly enhance riboswitch performance in haloarchaea.
• Engineered riboswitches offer a viable tool for constructing sophisticated genetic circuits in extremophilic archaea.