Temperature-sensitive Poliovirus Mutants Defective in Repression of Host Protein Synthesis are also Defective in Structural Protein

Wild-type poliovirus (ts +) rapidly represses ynthesis of host cell protein (psr+ character), at permissive (37 °C) or restrictive (39"5 °C)temperatures. A search for ts mutants that were psr+ at 37 °C and psr at 39"5 °C was successful when gene expression was minimized by adding guanidine, depleting cystine and avoiding very high input multiplicities. Repressor defects were found in six ts mutants, all of which carry ts defects olely in structural protein. All of the five ts mutants tested that were defective in non-structural genes failed to show a repressor defect. The repressor defect was confirmed to lie in structural genes by showing that three out of four independent ts + revertants from a structural protein (psr. ts) mutant were also psr +. Thus repression is dependent on the configuration of a product of the structural protein gene. These findings are discussed in terms of the equestron, a hypothetical poliovirus regulator