Co-Transcriptional Molecular Assembly Results in a Kinetically Controlled Irreversible RNA Conformational Switch.

Co-transcriptional RNA folding results in dynamic behavior of RNA transcripts. Extra stimuli can perturb the stability of the nascent RNA and alter its conformation and function. Here, an artificial RNA conformational switch, which consists of a 5' aptamer unit for sensing thiamine pyrophosphate (TPP) and a 3' working unit (TAR RNA) that binds Tat peptide connected by a switching sequence, was designed and cotranscriptionally functionalized. Co-transcriptional binding of TPP induced an RNA conformational change that allowed interaction of Tat peptide and the TAR RNA unit. Two conformational states, which are mutually exclusive depending on the TPP binding, did not show post-transcriptional interconversion. The irreversible RNA conformational switch demonstrated here, which kinetically coupled co-transcriptional RNA folding and molecular assembly in nonequilibrium biological systems, will enable efficient switching of RNA functions applicable for constructing intracellular molecular sensors.