Gene expression control by Bacillus anthracis purine riboswitches.

In all kingdoms of life, cellular replication relies on the presence of nucleosides and nucleotides, the building blocks of nucleic acids and the main source of energy. In bacteria, the availability of metabolites sometimes directly regulates the expression of enzymes and proteins involved in purine salvage, biosynthesis, and uptake through riboswitches. Riboswitches are located in bacterial mRNAs and can control gene expression by conformational changes in response to ligand binding. We have established an inverse reporter gene system in Bacillus subtilis that allows us to monitor riboswitch-controlled gene expression. We used it to investigate the activity of five potential purine riboswitches from Bacillus anthracis in response to different purines and pyrimidines. Furthermore, in vitro studies on the aptamer domains of the riboswitches reveal their variation in guanine binding affinity ranging from namomolar to micromolar. These data do not only provide insight into metabolite sensing but can also aid in engineering artificial cell regulatory systems.