Viruses as environmental mutagenic factors

Injections into Drosophila melanogaster males of 9 DNA- and RNA-containing viruses non-infectious for this insect, proved that all of them are highly mutagenic, inducing numerous gene mutations or microdeletions but no gross chromosome rearrangements. Relatively few specific loci are affected, they vary per virus, and the mutation rate for such a locus is extraordinarily high. These peculiarities of the mutagenic action of viruses closely resemble those of the mutagenic action of exogenous non-viral DNA earlier studied by the author and his co-workers. It was shown that the mutagenic element of a virus is its nucleic acid; viral proteins completely lack mutagenic properties. Virus-induced gene mutations are probably due to insertions of fragments of viral DNA (or cDNA) into the host chromosomes; at least some of these mutations are capable of transpositions and reversions. On the other hand, chromosome aberrations which arise in virus-infected cells are evidently produced secondarily by pathological disturbances of metabolic processes in the infected cells. Our results and literature data lead to the conclusion that a significant share of hereditary defects in man might be caused by viruses, even by those apathogenic for humans, particularly by attenuated live viral vaccines. It is, therefore, important to work on the creation of purely proteinaceous viral vaccines free from nucleic acids and thus genetically safe. The hazards of viral mutagenesis should also be kept in mind when preparing recombinant DNA molecules used in genetic engineering.