Prereplicative events involving simian virus 40 DNA in permissive cells.

Simian virus 40 DNA molecules were found to be unable to replicate for 9 h after infection, even in cells that were already replicating the DNA of preinfecting simian virus 40; after 9 h, the ability of the DNA to replicate began to rise sharply. The kinetics of activation indicated that each DNA molecule undergoes a series of slow consecutive reactions, not involving T-antigen, before it can replicate. These pre-replicative molecular transformations probably involve configurational changes; their nature and their relation to the initiation of viral DNA synthesis is discussed. Observation of the replicative behavior of one viral DNA in the presence of another was made possible by the use of two different mutants with distinguishable DNAs: a viable deletion mutant containing DNA insensitive to TAqI restriction enzyme was used to provide viral functions required for replication, and a tsA mutant with TaqI-sensitive DNA was introduced at various times as a probe to determine the ability of the DNA to replicate under different conditions.