DISTRIBUTION OF DRUG-RESISTANCE MUTATIONS IN TYPE-3 POLIOVIRUS IDENTIFIES 3 REGIONS INVOLVED IN UNCOATING FUNCTIONS

We have previously described the use of an uncoating inhibitor, WIN 51 711, to select drug-resistant mutants of the Sabin strain of polioviru s type 3. Two-thirds of the mutants proved to be dependent on the drug for plaque formation because of extreme thermolability (A. G. Mosser and R. R. Rueckert, J. Virol. 67:1246-1254, 1993). Here we report the responsible mutations; all were traced to single amino acid substituti ons. Mutations conferring dependence and thermolability occurred in al l four capsid proteins (VP1 to VP4), but all were clustered near resid ue 53 of VP4 at the inner capsid surface. Amino acid substitutions of the remaining non-drug-dependent mutants were mapped to three distinct loci: (i) on or near the inner capsid surface, at VP4 residue 46 or V P1 residue 129, in the vicinity of the drug dependence substitutions; (ii) at residues 192, 194, and 260 in the lining of the VP1 beta barre l, which is the drug-binding site; and (iii) at VP1 residue 105 on the edge of the canyon surrounding the fivefold axis of symmetry, the put ative receptor-binding site. Ah of the mutations increased the eclipse rate of cell-attached virus. Such mutants help identify parts of the capsid that play a role in viral uncoating functions.