Diversity and modularity of tyrosine-accepting tRNA-like structures.

Certain positive-sense single-stranded RNA viruses contain elements at their 3' termini that structurally mimic tRNAs. These tRNA-like structures (TLSs) are classified based on which amino acid is covalently added to the 3' end by host aminoacyl-tRNA synthetase. Recently, a cryoEM reconstruction of a representative tyrosine-accepting tRNA-like structure (TLS) from brome mosaic virus (BMV) revealed a unique mode of recognition of the viral anticodon-mimicking domain by tyrosyl-tRNA synthetase. Some viruses in the genus of are also selectively aminoacylated with tyrosine, yet these TLS RNAs have a different architecture in the 5' domain that comprises the atypical anticodon loop mimic. Herein, we present bioinformatic and biochemical data supporting a distinct secondary structure for the 5' domain of the TLS compared to those in Despite forming a different secondary structure, the 5' domain is necessary to achieve robust in vitro aminoacylation. Furthermore, a chimeric RNA containing the 5' domain from the BMV TLS and the 3' domain from a TLS are aminoacylated, illustrating modularity in these structured RNA elements. We propose that the structurally distinct 5' domain of the TLSs performs the same role in mimicking the anticodon loop as its counterpart in the BMV TLS Finally, these structurally and phylogenetically divergent types of TLS provide insight into the evolutionary connections between all classes of viral tRNA-like structures.