ABSTRACT

RNA recombination is of interest for several reasons. First, it offers a means of manipulating RNA genomes, e.g., for genetic mapping. Second, the ability to exchange genetic information may confer a selective advantage on the virus and thus be a significant factor in its evolution. Third, although homologous recombination was reported in poliovirus, only recently has the process been studied in molecular terms. Nonhomologous recombination has been reported in two positive strand RNA viruses, Sindbis and brome mosaic virus. Studies on polioviruses vaccines show that recombination can occur in the infected animal. O. M. Kew and B. K. Nottay estimate that out of the approximately 10 cases of vaccine-associated poliomyelitis per year in the US, 15% involve intertypic recombinants. Homologous recombination was first demonstrated in poliovirus by G. K. Hirst and N. Ledinko in the early 1960s. Since the poliovirus replicative intermediate is singlestranded in vivo, the growing RNA strand must unwind from its template as it is synthesized.