GENE-EXPRESSION FROM VIRAL-RNA GENOMES

'This review is centered on the major strategies used by plant RNA vir uses to produce the proteins required for virus multiplication. The st rategies at the level of transcription presented here are synthesis of mRNA or subgenomic RNAs from viral RNA templates, and 'cap-snatching' . At the level of translation, several strategies have been evolved by viruses at the steps of initiation, elongation and termination, At th e initiation step, the classical scanning mode is the most frequent st rategy employed by viruses; however in a vast number of cases, leaky s canning of the initiation complex allows expression of more than one p rotein from the same RNA sequence. During elongation, frameshift allow s the formation of two proteins differing in their carboxy terminus. A t the termination step, suppression of termination produces a protein with an elongated carboxy terminus. The last strategy that will be des cribed is co- and/or post-translational cleavage of a polyprotein prec ursor by virally encoded proteinases. Most (+)-stranded RNA viruses ut ilize a combination of various strategies.