GENOME ORGANIZATION OF GRAPEVINE FANLEAF NEPOVIRUS RNA2 DEDUCED FROM THE 122K POLYPROTEIN P2 IN-VITRO CLEAVAGE PRODUCTS

The full-length transcript of grapevine fanleaf virus (GFLV) RNA2 prod uces a primary product of 122K when translated in the rabbit reticuloc yte system. This 122K polyprotein is completely processed in vitro by the RNA1-encoded 24K proteinase. The positions of the cleavage sites w ithin the polyprotein have been mapped and the genome organization of GFLV-F13 RNA2 has been established. The order of mature proteins in th e 122K polyprotein is the amino-terminal 28K protein, the 38K protein followed by the 56K coat protein at the carboxy terminus. These protei ns represent the final cleavage products of the 122K polyprotein. A 66 K protein which yields 28K and 38K proteins constitutes the major matu ration intermediate. Microsequencing of the amino extremity of radioac tively labelled 38K protein allowed identification of the Cys257/Ala25 8 site as the cleavage site recognized by the GFLV proteinase between the 28K and the 38K proteins in the 66K protein in addition to the Arg 605/Gly606 site between the 38K protein and the coat protein.