DNA of simian virus 40 mutates Chinese hamster cells

Infection of Chinese hamster cells with SV 40 DNA gives rise to mutants resistant both to S-axaguanine (AG) and aminopterin (AP). This mutagenic effect can be raised when facilitating DNA uptake of cells by a helper agent. The extent of muyagenic action depends further on the concentration of DNA applied to the cells, with 2 micrograms/ml being more effective than 10 micrograms/ml, as well as on the period of incubation of infected cells before onset of mutant selection (mutation expression time). Using the AG resistance marker the mutation frequency can be increased more than 8-fold compared with the spontaneous mutation frequency. Reconstituted SV 40 minichromosomes show a mutagenic action which is similar to the DNA-mediated mutagensis whereas non-viral DNA from mammalian cells fails to induce mutations significantly. A major part of isolated clones of SV 40-induced mutants tested so far does express SV 40 T-antigen, suggesting the persistence of SV 40 genetic material in these clones. The possible existence of relations between mutagenic and transforming capacities of SV 40 is discussed.