Increased rate of RNA synthesis: early reaction of primary mouse kidney cells to infection with polyoma virus of simian virus 40.

The rate of transcription in isolated nuclei of primary mouse kidney cells increases by a factor of about 1.5 between 5 and 8 h after infection with polyoma virus or simian virus 40. This process requires intact virus and is inhibited by cycloheximide and actinomycin D. It appears to involve the activity of all three nuclear RNA polymerases, and evidence was obtained for an increase in the rate of synthesis of most, if not all, species of RNA that were already produced in resting cells before infection. The additional synthesis of a few new RNA species not made in uninfected cells, however, cannot be excluded. The increase in the rate of transcription seems to precede an increase in the rate of translation in infected cells. Our additional finding that large and small tumor antigens (T-antigens) are synthesized at the same time after infection suggests that these cellular reactions are early consequences of the action of one or both of these T-antigens in the infected cell. Experiments with simian virus 40 mutants provided strong evidence for an involvement of large-T-antigen but not of small t-antigen. These studies furthermore indicate that the increase in the transcription rate is a prerequisite for the induction of DNA replication in simian virus 40-infected mouse kidney cells.