Confirmation of the constitution of alfalfa mosaic virus hybrid genomes by backcross experiments

Plant-virus-based vectors for gene transfer will be of limited use because of the high error frequency during viral RNA synthesis

The error frequency during the RNA replication of alfalfa mosaic virus (AMV) was calculated to be significantly higher than 10(-5). It may be expected that RNA synthesis in general will have low fidelity compared to DNA synthesis. The low fidelity of RNA replication will severely restrict the usefulness of vectors for genetic engineering which are based on RNA viruses, viroids or DNA viruses which are replicated via an RNA intermediate (e.g. caulimoviruses). Spontaneous mutants selected by host shift were found to be much less stable than UV-induced mutants. This difference points to variations in fidelity during RNA synthesis, probably due to the local sequence of the template.

Further genetic analysis of a temperature-sensitive mutant of cowpea mosaic virus

The two reciprocal hybrids of wild-type cowpea mosaic virus (Sb) and the temperature-sensitive mutant N168 were constructed. Symptoms of both hybrids differed from those of the parent strains in three differential hosts indicating that N168 carries mutations in both components and that symptoms result from interactions between components. The occurrence of one or more temperature-sensitive mutations in the middle-component RNA was confirmed. In vitro recombination of the hybrids yielded isolates indistinguishable from the parent strains.