Riboregulators

After observing the many and varied naturally occuring post-transcriptional, regulatory RNA systems, Isaacs et al. designed and engineered a modular synthetic system where RNA turns on and off gene expression by controlling translation. The modularity of their system allows any gene to be regulated instead of only a specific gene to which the riboregulator is targeted.

Design

The design itself has two components: a short cis-repressed RNA sequence (crRNA) that is inserted upstream of the gene and a transactivating RNA sequence (taRNA) that targets the crRNA. The crRNA sequence contains two fundamental components: the complement of the ribosomal binding site (RBS) and a pyrimidine-uracil-nucleotide-purine (YUNR) sequence. When not interacting with the taRNA, the complement of the RBS binds to the RBS, causing the crRNA to loop and block the ribosome's access to the RBS. When the RBS is blocked, translation does not occur; the gene expression is off. The YUNR sequence has a complement on the taRNA. When the taRNA finds a crRNA, the interaction with the YUNR sequence begins pulling the crRNA off the RBS.

The taRNA is free floating and regulated by an inducible promoter. The inducible promoter allows the researcher to determine under what conditions gene expression will be turned on. Besides the complement to the YUNR sequence, the taRNA contains a section of high complementarity to section of the crRNA that folds over to cover the RBS, which allows the taRNA to keep the crRNA sequestered from the RBS.

To recap, gene expression is off when there is crRNA upstream of the gene but no taRNA is in the system. In the presence of taRNA, gene expression is turned back on.