WIN51711-resistant mutants of poliovirus type 3: capsid residues important in uncoating functions.

Capsid-binding drugs that inhibit the first stage of picornaviral uncoating were used to select drug-resistant mutants of the Sabin strain of poliovirus type 3. Such mutants provide information about parts of the capsid that are important for functions blocked by the drugs, and also about pathways to drug resistance. Amino-acid substitutions allowing virus to produce progeny in the presence of drug were mapped to 13 different residues occupying three distinct locations: (I) the canyon base; (II) the lining of the drug-binding pocket; and (III) the base of the protomer. These loci might be thought of as action points for transmitting the uncoating signal from receptor, through the pocket, and to the base of the protomer. All of the mutations in a special class of drug-dependent mutants were clustered at site (III) and all were hyperlabile, i.e., uncoated spontaneously (without receptor) at growth temperature unless prevented from doing so by the presence of drug in the pocket. Thus, site (III) seems to represent a kind of thermostat which regulates the temperature at which the uncoating transition (release of VP4 to form A particles) is triggered.