THE 5' UNTRANSLATED REGION OF PVY RNA, EVEN LOCATED IN AN INTERNAL POSITION, ENABLES INITIATION OF TRANSLATION

Potato virus Y (PVY) is the type member of the potyvirus group. Potyviruses, like picorna-, como-, and nepoviruses, belong to the picornavirus-like supergroup. All these viral RNAs have a VPg at their 5' end, and for four picornaviruses and one comovirus internal initiation of translation has been reported. To know if such a translational mechanism holds true for potyviral RNAs, the 5' nontranslated region (NTR) of PVY RNA was placed in an internal position, either by adding 91 bases upstream of the PVY 5'NTR or by inserting the PVY 5'NTR into an intercistronic region. The addition of extra bases stimulates translation in a rabbit reticulocyte lysate, and the presence of the PVY 5'NTR in the intercistronic region allows the synthesis of the second cistron. These findings strongly suggest that PVY RNA initiates translation by an internal ribosome-binding mechanism. Furthermore, the use of antisense oligodeoxynucleotides indicates that the entire 5'NTR seems to be involved in such a mechanism.