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Many RNA viruses encode more than one gene on a single genomic RNA. Yet only the first gene, or open reading frame (ORF), on a normal eukaryotic mRNA is translated. Thus, downstream genes on viral genomes are expressed either via novel translational events or, more commonly, by deployment of subgenomic mRNAs (sgRNAs). Subgenomic RNAs of positive-strand viruses have the same 3! ends as genomic RNA, but have deletions at the 5! ends to bring the 5! end of the RNA in proximity with the start codon of downstream (on genomic RNA) ORFs. Because replication is required for sgRNA synthesis, the RNA-dependent RNA polymerase (RdRp) is always translated first, directly from genomic RNA of positive-strand RNA viruses. sgRNAs express products needed during intermediate and late stages of infection, such as structural or movement proteins. Taxa of (+) sense viruses that produce sgRNAs …