Construction and properties of intertypic poliovirus recombinants: first approximation mapping of the major determinants of neurovirulence.

An attempt was made to map, in a general way, the region of the poliovirus genome that is responsible for the neurovirulent and attenuated phenotypes of different virus strains. A set of four recombinants was investigated, one described previously (E. A. Tolskaya, L. I. Romanova, M. S. Kolesnikova, and V. I. Agol, 1983, Virology 124, 121-132) and three obtained in the present work with the following genetic structure: a 5' end-adjacent segment of the genome derived from either a virulent strain (452/62 3D), or from an attenuated strain (Leon-2) of poliovirus type 3, the remaining RNA sequences being derived from either a virulent strain (Mgr), or an attenuated strain (LSc-gr3) of poliovirus type 1. The crossover points in the recombinant genomes were centrally located, somewhere between the gene(s) that determines antigenic specificity of the virus and the locus that determines resistance of virus multiplication to low doses of guanidine. The recombinant nature of the newly selected clones was definitively established by mapping RNase T1 oligonucleotides of their genome. The recombinants were characterized with respect to their ability to produce infectious progeny and synthesize viral RNA at an elevated temperature. Neurovirulence of the recombinants was assayed by intracerebral inoculation of monkeys. Irrespective of the origin of the 3' end-adjacent segment of the genome, the recombinants that inherited the 5' end-adjacent segment from the neurovirulent parent were neurovirulent, whereas the recombinants with the 5' end-adjacent segment derived from the attenuated parent were not. The results suggest that the major determinants of neurovirulence of these recombinants (and by inference, of their parental viruses) reside in the 5' end-adjacent segment of poliovirus genome, known to code for capsid proteins.