Investigation of the 5' terminal structures of genomic and subgenomic RNAs of potato virus S.

Hybrid arrest translation involving an antisense RNA, generated from a cloned cDNA close to the 5' region of potato virus S genomic RNA, blocked the synthesis of genomic encoded products but had little effect on subgenomic RNA encoded products. Similarly, the synthesis of PVS genomic RNA-directed peptides was inhibited by the cap analogue m7G5'ppp5'G, suggesting the presence of a cap structure at the 5' terminus whilst subgenomic RNA encoded products remained unaffected, suggesting an uncapped structure. This was confirmed by artificially produced uncapped subgenomic RNAs translating as efficiently in in vitro translation systems as authentic viral subgenomic RNAs.