EVOLUTION OF MULTIPLE GENOME MUTATIONS DURING LONG-TERM PERSISTENT INFECTION BY VESICULAR STOMATITIS-VIRUS

Persistent infection of BHK21 cells was established with cloned vesicular stomatitis virus plus purified DI particles and maintained in vitro for over 5 years. After 1 year of persistence, the infectious virus RNA genome had evolved several oligonucleotide map changes, and numerous changes had accumulated by 3.5 years. Additional evolution occurred by the fourth year and continued until the fifth year. The contrast, repeated passage of virus in acute infections of several cell types in vitro or in vivo did not lead to detectable oligonucleotide map changes. The short DI particle originally used to co-infect with infectious virus in establishing persistent infection has been displaced by an ever present and constantly changing population of other DI particles of differing sizes and radically differing oligonucleotide maps. We conclude that the genomes of both infectious VSV and its DI particles undergo continuous evolutionary change during years of persistence. In the infectious virus, these changes involve hundreds of mutations which are usually expressed as poorly replicating, temperature-sensitive, small plaque mutants. These are stable mutants which do not revert to wild-type when passaged repeatedly in acute infections at 37 or 33°C. It appears that the sequestered intracellular environment of persistently infected cells favors rapid and continuous virus evolution. © 1979.