THE 2 NONSTRUCTURAL PROTEINS FROM WHEAT DWARF VIRUS INVOLVED IN VIRALGENE-EXPRESSION AND REPLICATION ARE RETINOBLASTOMA-BINDING PROTEINS

Tumor-inducing viruses like simian virus 40 or the human adenovirus pr oduce oncoproteins which interfere with the cellular retinoblastoma (R b) tumor-suppressor protein to create an appropriate molecular environ ment in the nucleus for viral transcription and replication. Such a st rategy has been considered to be restricted to animal viruses. Hers we demonstrate that plant viruses may use similar mechanisms for recruit ing host factors. Wheat dwarf virus (WDV) encodes two potential nonstr uctural proteins, C1 and C1:C2, both containing the consensus Rb-bindi ng motif LeuXCysXGlu that allows the oncoproteins from animal viruses to inactivate Rb. C1:C2 is a key determinant of viral replication and V(virion)-sense expression. Using a yeast two-hybrid protein assay, we demonstrate for the first time that the C1:C2 protein from WDV intera cts with a retinoblastoma protein, providing an explanation for the pr eviously observed dependence of viral replication on an intact Rb-bind ing motif. We also show that C1, for which no function had been demons trated, is required for V-sense gene expression. This suggests that V- sense expression might be dependent on the interaction of C1 with Rb. Our findings provide further evidence for the presence of transforming -like proteins in a plant virus and will help to explain the productio n of symptoms in a plant viral infection through a mechanism mediated by a key regulator of cell cycle and differentiation. (C) 1996 Academi c Press, Inc.