SUMMARYRecombinant and parental poliovirus particles were indistinguishable by ratezonal and isopycnic sedimentation, and by u.v. inactivation. Sensitive selective procedures, applied to ts + recombinants to detect genetic segregation of one parent, failed to reveal any. Poliovirus genetic recombinant particles thus appear to be conventional virus particles; their significance for recombination mechanisms is discussed. Sensitivity to the growth inhibitor 2-(3-chloro-p-tolyl)-5-ethyl-l,3,4-oxadiazole is shown to depend on a product of the structural protein gene.
A labile subviral particle (‘the equestron’) is proposed as a multifunctional regulator of poliovirus growth, withaffinities for 45s ribosomal subunits and 5’ ends of viral RNA. These suggested properties suffice to explain suppression of hostprotein synthesis, synchronous synthesis of viral RNA and protein, and timing of maturation. The candidate for the equestron is a precursor to the virionstructural unit.
SUMMARYWild-type poliovirus (ts +) rapidly represses synthesis 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 solely 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.
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