The role of the transforming A gene of SV40 in the mutagenic activity of the virus.

The mutagenic activity of the tsA239 mutant of SV40 which synthetizes a defective T antigen at 40 degrees C was investigated in Chinese hamster cells under permissive and nonpermissive temperature. At 33 degrees C the virus increased the yield of 6-mercaptopurine-resistant colonies after 2 days expression time by a factor of 1.6-4 as compared with the control and raised the frequency of aberrant metaphases after the same time by a factor of 1.9-3.4. In the same experiments, with the same initially infected population of Chinese hamster cells, at 40 degrees C tsA SV40 did not induce either gene mutations or chromosome aberrations at the same early stage after infection. Presumably the activity of the A gene of SV40 is necessary not only for the transforming but also for the mutagenic effect of the virus.