We are developing an in vitro system for poliovirus RNA recombination. In this system, two mutant RNAs are replicated with poliovirus RNA-dependent RNA polymerase. Recombination will produce RNAs containing neither mutation and will be the only progeny RNAs that are infectious. We will use this system to determine what proteins and reaction conditions are required for recombination and to study the details of the mechanism of recombination.