Sequential action of a tRNA base editor in conversion of cytidine to pseudouridine

Post-transcriptional RNA editing modulates gene expression in a condition-dependent fashion. We recently discovered C-to-psi editing in Vibrio cholerae tRNA. Here, we characterize the biogenesis, regulation, and functions of this previously undescribed RNA editing process. We show that an enzyme, TrcP, mediates the editing of C-to-U followed by the conversion of U to psi, consecutively. AlphaFold-2 predicts that TrcP consists of two globular domains (cytidine deaminase and pseudouridylase) and a long helical domain. The latter domain tethers tRNA substrates during both the C-to-U editing and pseudouridylation, likely enabling a substrate channeling mechanism for efficient catalysis all the way to the terminal product. C-to-psi editing both requires and suppresses other modifications, creating an interdependent network of modifications in the tRNA anticodon loop that facilitates coupling of tRNA modification states to iron availability. Our findings provide mechanistic insights into an RNA editing process that likely promotes environmental adaptation. C-to-psi conversion is a previously uncharacterized form of base editing. Here, the authors describe how the TrcP enzyme catalyzes this process in a stepwise fashion and how this editing process is controlled by a network of modifications and nutrient availability to optimize translation efficiency.

Automated summary

This study characterizes the C-to-psi conversion RNA editing process and its regulation, highlighting the role of the TrcP enzyme and modification network in optimizing translation efficiency.