Substitution in the poliovirus replicase gene determines actinomycin D sensitivity of viral replication at elevated temperature.

A series of ts+ revertants and recombinants derived from a temperature-sensitive plurimutant of poliovirus type 1 showed identical plaquing efficiencies at 37 degrees C and at 39 degrees C and exhibited similar yields and plaque morphology to wild-type virus. However, these viruses were characterized by clear inhibition of viral RNA synthesis at 39 degrees C, as measured by uridine incorporation in the presence of actinomycin D. Similarly, virus yields were decreased by one log in the presence of actinomycin D during infection at 39 degrees C. All the ts+ recombinants formed between temperature-sensitive mutants of poliovirus that were inhibited by actinomycin D carried a glutamine----histidine modification at residue 170 of their viral replicase (polypeptide 3D), due to a G----U substitution at nucleotide 6496. Inhibition of viral growth was increased by pretreatment of cells with actinomycin D for 3 h prior to infection, suggesting that actinomycin D sensitivity could reflect an increased dependence of viral RNA replication on host factor(s).