Interference in SV40 DNA infections: a possible basis for cellular competence.

At the restrictive temperature, DNA from temperature-sensitive mutants of simian virus 40 (SV40) (in the A or B/C genes) interferes with plaque formation by wild-type SV40 DNA. This interference occurs early in the first cycle of infection. Nonhomologous DNA also can interfere with SV40 DNA infection. The mode of interference by ts SV40 DNAs and nonhomologous DNAs appears to be the same. In conjunction with other observations the interference by nonhomologous DNA and the similarity of interference by tsA DNA and tsB DNA suggest that interference does not require expression of any viral gene product. Since interference is observed even when the infections by interfering DNA and wild-type DNA are separated in time, interference must occur after the DNAs interact with cells. Furthermore, the different efficiencies with which structurally similar DNAs (SV40, PM2 and φX174 replicative form) interfere indicate that interference depends at least in part on nucleotide sequence. Those two observations suggest that interference is an intracellular, perhaps nuclear, phenomenon. The possible relevance of this interference phenomenon to observations on cellular competence for SV40 DNA infections is discussed.