Studies on the Genome Structure of Neurovirulent and Attenuated Polioviruses

The RNA genomes of neurovirulent and attenuated type 3 polioviruses have been cloned in E. cola using an efficient RNA.cDNA hybrid technique. The complete nucleotide sequence of the vaccine-associated neurovirulent revertant P3/119 and, in collaboration with others, the attenuated vaccine strain P3/Leon 12 a1b, have been determined. These have been compared with that of the neurovirulent parent strain P3/Leon/3 7. Ten nucleotide sequence differences were observed between the parent P3/Leon/37 and the vaccine P3/Leon 12 a1b, three of which resulted in amino acid substitutions. Between the vaccine and the revertant P3/119, seven nucleotide sequence differences were observed. Three of these resulted in amino acid substitutions. The possible significance of individual nucleotide sequence differences to the attenuation of and reversion to neurovirulence in poliovirus type 3 is discussed. The nucleotide sequence of P3/Leon 12 a1b was the first to be determined for a type 3 poliovirus. Comparison of this sequence with published type 1 sequences has demonstrated the extent of the molecular homology between them.