The biological function and mutual dependence of bottom component and top component a of alfalfa mosaic virus

Purified bottom component RNA from one strain of alfalfa mosaic virus and purified top component a RNA from a different strain are not infectious or only minimally infectious when inoculated alone, but when a mixture of the two RNA's is inoculated, enhanced infectivity is found. The progenies of single lesions produced from combined inocula were isolated. These isolates show biological and physical properties from both initial strains. Their serological reactions and biological properties exclude the possibility that these isolates are mixtures. The bottom component RNA and the top component a were isolated from one of these isolates and combined with top component a and bottom component RNA, respectively, from the strains to which they belonged originally. Isolates obtained from these combinations are indistinguishable from the initial strains. Apparently the RNA's are not altered when they are replicated in the presence of an RNA from a different strain. These results indicate that at least two components are necessary for an infection with alfalfa mosaic virus. These components are mutually dependent.