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.