DELETION OF THE C-TERMINAL-33 AMINO-ACIDS OF CUCUMBER MOSAIC-VIRUS MOVEMENT PROTEIN ENABLES A CHIMERIC BROME MOSAIC-VIRUS TO MOVE FROM CELL-TO-CELL

The movement protein (MP) gene of brome mosaic virus (BMV) was precise ly replaced with that of cucumber mosaic virus (CMV). Infectivity test s of the chimeric BMV on Chenopodium quinoa, a permissive host for cel l-to-cell movement of both BMV and CMV, showed that the chimeric BMV f ailed to move from cell to cell even though it replicated in protoplas ts. A spontaneous mutant of the chimeric BMV that displayed cell-to-ce ll movement was subsequently obtained from a local lesion during one o f the experiments. A cloned cDNA representing the genomic RNA encoding the MP of the chimeric BMV mutant was analyzed and found to contain a mutation in the CMV MP gene resulting in deletion of the C-terminal 3 3 amino acids of the MP. Directed mutagenesis of the CMV MP gene shelv ed that the C-terminal deletion was responsible for the movement capab ility of the mutant. When the mutation was introduced into CMV, the CM V mutant moved from cell to cell in C. quinoa, though the movement was less efficient than that of the wild-type CMV. These results indicate that the CMV MP, except the C-terminal 33 amino acids, potentiates ce ll-to-cell movement of both BMV and CMV in C. quinoa. In addition, sin ce C. quinoa is a common host for both BMV and CMV, these results sugg est that the CMV MP has specificity for the viral genomes during cell- to-cell movement of the virus and that the C-terminal 33 amino acids o f the CMV MP are involved in that specificity.