Fig. 1.
Illustration of the BSMV genomic and subgenomic RNAs. RNAα serves as the mRNA for the αa protein, which contains the capping and helicase subunits of the RNA-dependent RNA polymerase (RdRp). RNAβ encodes the βa protein (coat protein) and the “triple gene block” composed of the TGB1, TGB2, TGB2′, and TGB3 proteins. The βa protein is translated from the genomic RNA; the TGB1 protein is expressed from sgRNAβ1 and the TGB2, TGB2′, and TGB3 proteins are translated from sgRNAβ2. The genomic RNAγ serves as a messenger for translation of the γa polymerase subunit of the RdRp and encodes the γb protein, which is expressed from sgRNAγ. All genomic and subgenomic RNAs are capped (black circle) at the 5′ terminus, contain an internal poly (A) tail (An), and possess a conserved tRNA-like structure (black rectangle) at the 3′ terminus.