| Abstract: | The effects of mutations in 5' the noncoding region (NCR) of a recombinant strain of poliovirus MAS 27 plaque 1 on neurovirulence were determined during persistent infection in the mouse central nervous system (CNS). Persistent virus isolates were recovered from the CNS of mice to determine the influence of specific sequence alterations in the 5' NCR on neurovirulence and to correlate the regulation of neurovirulence and expression of poliovirus genome at the molecular level. The influence of mouse genotype on persistent infection of poliovirus in the CNS was examined by both cytopathic effect (CPE) in vitro and by the polymerase chain reaction method. In DBA/1 and DBA/2 mice a mutant poliovirus was isolated by CPE and the RNA genome of poliovirus was detected by PCR. It was concluded that non H-2 gene may affect the persistent infection of poliovirus in the mice. Thirteen in vivo derived viral mutants were recovered from the brains of mice. In addition, polioviral genomic RNA was detected from the brain of a mouse at day 282 PI by PCR, which supports the hypothesis that poliovirus infects persistently in the CNS of mice. Nucleotide sequence analysis of MAS 27C revealed that position 472 had back-mutated to the wild type (cytosine), whereas base 537 remained guanine; MAS 27U remained guanine at position 472, but had mutated at position 537 from guanine to uracil. MAS 27G had guanine at position 472, but mutated from guanine at position 537 to cytosine. Attenuated mutants such as MAS 27G and MAS 27U were at least 100,000 fold less virulent than the MAS 27C revertant; the translation of the RNA of both attenuated mutants was less efficient than MAS 27C revertant. The data may provide evidence for a specific nucleotide sequence regulatory element for protein synthesis of the virus and its neurovirulence. MAS 27G showed that the base pairing guanine at position 472 and cytosine at position 537 has greater possibilities for the mutation selection and of maintenance of the stable attenuation phenotype. The stable attenuated base paired MAS 27G poliovirus might be, therefore, a good candidate for a new stable attenuated type 3 poliovaccine. |
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