An RNA tertiary switch by modifying how helices are tethered.
Bottom Line: A viral tRNA-like structure has evolved a unique strategy to undergo a tertiary structure conformational switch that may help regulate viral regulation.
A viral tRNA-like structure has evolved a unique strategy to undergo a tertiary structure conformational switch that may help regulate viral regulation.
License 1 - License 2
Mentions: Early on, it was unclear whether the TLS could indeed adopt a tRNA-like conformation because it lacked many characteristic features of canonical tRNA sequences. The TLS secondary structure determined using nuclease probing data  subsequently revealed how the TLS achieved a tRNA-like fold and highlighted some important differences from canonical tRNA particularly at the acceptor stem, which is the site of aminoacylation . In canonical tRNA, the acceptor stem is formed by base pairing of residues in the 5’ and 3’ ends of tRNA (Figure 1a). The TLS features a truncated 5’ strand that is not involved in canonical pairing with the 3’ strand (Figure 1b). This presumably is important to free up the 5’ end to link up with the rest of the viral genome without sterically obstructing the 3’ end. The longer 3’ strand was then proposed  to adopt a so-called ‘pseudoknot’ - an RNA motif in which a single strand folds back on itself to form two helical stems in such a way that the strand termini are located on opposite ends of the motif. This makes it possible to create an acceptor-like stem out of the 3’-terminus that can be aminoacylated (Figure 1b).Figure 1