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 produces a primary product of 122K when translated in the rabbit reticulocyte system. This 122K polyprotein is completely processed in vitro by the RNA1-encoded 24K proteinase. The positions of the cleavage sites within the polyprotein have been mapped and the genome organization of GFLV-F13 RNA2 has been established. The order of mature proteins in the 122K polyprotein is the amino-terminal 28K protein, the 38K protein followed by the 56K coat protein at the carboxy terminus. These proteins represent the final cleavage products of the 122K polyprotein. A 66K protein which yields 28K and 38K proteins constitutes the major maturation intermediate. Microsequencing of the amino extremity of radioactively labelled 38K protein allowed identification of the Cys257/Ala258 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 Arg605/Gly606 site between the 38K protein and the coat protein.