A mutant of alfalfa mosaic virus with an unusual structure.

A spontaneous mutant of alfalfa mosaic virus (AMV) with an altered structure is described. By analysis of pseudorecombinants the mutation(s) responsible for the altered structure were assigned to RNA 3. By in vitro translation and serology it is shown that both proteins (35K protein and coat protein) encoded by RNA 3 are changed. The mutation(s) present in RNA 3 also have an effect on the ratio of the three genomic RNAs, both in virion as well as in double-stranded RNA preparations. Compared to wild-type particles mutant particles (1) have a lower electrophoretic mobility in polyacrylamide gels, (2) have a greater sedimentation velocity in sucrose density gradients, (3) do contain the same percentage of RNA, (4) are more prone to aggregation, (5) are somewhat less stable during storage, and (6) are less sensitive to uncoating by AMV-RNA. Electron micrographs show that the mutant preparations contain some very long bacilliform particles, however the majority of the particles is spheroidal and bear a strong resemblance to the particles of the ilarviruses. The structural properties of this mutant support the classification of AMV as an ilarvirus.