CAPSID PROTEIN AND HELPER COMPONENT PROTEINASE FUNCTION AS POTYVIRUS CELL-TO-CELL MOVEMENT PROTEINS

The role of bean common mosaic necrosis potyvirus (BCMNV) and lettuce mosaic potyvirus (LMV) proteins was investigated in terms of their cap acity to function as viral movement proteins (MPs). Using Escherichia coil-expressed proteins and microinjection techniques, direct evidence was obtained that both the potyviral capsid protein (CP) and helper c omponent-proteinase (HC-Pro) function in this capacity, in that both p roteins (a) trafficked from cell to cell, (b) induced an increase in p lasmodesmal size exclusion limit, and (c) facilitated cell-to-cell mov ement of viral RNA. CP and HC-Pro mutants were also produced and used in microinjection experiments. Mutations in the core region of the CP either impaired (single and double amino acid substitution mutants) or abolished (triple amino acid substitution mutant) cell-to-cell moveme nt, as did C-terminal deletion mutants in HC-Pro. The BCMNV P1, Cl, Nl a, and Nlb proteins did not exhibit viral MP properties, but Nla and N lb proteins were found to accumulate within the nuclei of injected cel ls. These results further establish the multifunctional nature of the potyvirus CP and HC-Pro. (C) 1997 Academic Press.