Histidine-accepting tRNA-like structures. (A) Cartoon diagram of a TLS-containing +ssRNA viral RNA genome, with the 3′ TLS indicated with a dashed box. Gray shaded boxes indicate the ORFs in the capped viral genome. (B) Cartoon representations of tRNA and the three classes of TLS. (C) Phylogenetic distribution of tRNA-like structures in several +ssRNA plant virus genera. Tree is based on the concatenated viral methyl transferase, replicative RNA helicase, and RNA dependent RNA polymerase (Mtr-Hel-RdRp) sequence, adapted from King et al. (2012). Asterisks denote the presence of one or more tRNA-like structure classes in each viral genus. (D) Consensus sequence and secondary structural model of the 157 identified unique histidine-accepting tRNA-like structure sequences. Regions are labeled relative to their homology in a canonical tRNA, if present. PK2: pseudoknot 2 region, D*: putative D-loop analog, AC: anticodon arm, T: T-arm, PK1: pseudoknot 1 region, DN: discriminator nucleotide. The location of an A base speculated to substitute for the N−1 G in authentic tRNAHis is indicated.
