Differential increase in topoisomerase II in simian virus 40-infected cells.

The time course of expression of topoisomerase I, topoisomerase II, and simian virus 40 (SV40) large tumor (T) antigen was determined in whole-cell extracts of uninfected versus SV40-infected TC7 cells. After a minor increase, the level of topoisomerase I remained fairly constant throughout the time course in both uninfected and SV40-infected cells. In contrast, the level of topoisomerase II increased markedly in SV40-infected cells but not in uninfected cells following the appearance of SV40 T antigen.