The degree of attenuation of tick-borne encephalitis virus depends on the cumulative effects of point mutations.
An infectious clone (pGGVs) of the tick-borne encephalitis complex virus Vasilchenko (Vs) was constructed previously. Virus recovered from pGGVs produced slightly smaller plaques than the Vs parental virus. Sequence analysis demonstrated five nucleotide differences between the original Vs virus and pGGVs; four of these mutations resulted in amino acid substitutions, while the fifth mutation was located in the 3' untranslated region (3'UTR). Two mutations were located in conserved regions and three mutations were located in variable regions of the virus genome. Reverse substitutions from the conserved regions of the genome, R(496)-->H in the envelope (E) gene and C(10884)-->T in the 3'UTR, were introduced both separately and together into the infectious clone and their biological effect on virus phenotype was evaluated. The engineered viruses with R(496) in the E protein produced plaques of smaller size than viruses with H(496) at this position. This mutation also affected the growth and neuroinvasiveness of the virus. In contrast, the consequence of a T(10884)-->C substitution within the 3'UTR was noticeable only in cytotoxicity and neuroinvasiveness tests. However, all virus mutants engineered by modification of the infectious clone, including one with two wild-type mutations, H(496) and T(10884), showed reduced neuroinvasiveness in comparison with the Vs parental virus. Therefore, although the H(496)-->R and T(10884)-->C substitutions clearly reduce virus virulence, the other mutations within the variable regions of the capsid (I(45)-->F) and the NS5 (T(2688)-->A and M(3385)-->I) genes also contribute to the process of attenuation. In terms of developing flavivirus vaccines, the impact of accumulating apparently minor mutations should be assessed in detail.
Gritsun
T S
TS
Institute of Virology and Environmental Microbiology, Mansfield Road, Oxford OX1 3SR, UK1.
Desai
A
A
Institute of Virology and Environmental Microbiology, Mansfield Road, Oxford OX1 3SR, UK1.
Gould
E A
EA
Institute of Virology and Environmental Microbiology, Mansfield Road, Oxford OX1 3SR, UK1.
D020413:3' Untranslated Regions / Q000235:genetics; D019943:Amino Acid Substitution; D000818:Animals; D002213:Capsid / Q000235:genetics; D004669:Encephalitis Viruses, Tick-Borne / Q000235:genetics / Q000472:pathogenicity*; D004675:Encephalitis, Tick-Borne / Q000517:prevention & control; D006801:Humans; D051379:Mice; D010641:Phenotype; D017354:Point Mutation; D014613:Vaccines, Attenuated; D014759:Viral Envelope Proteins / Q000235:genetics; D017361:Viral Nonstructural Proteins / Q000235:genetics; D014765:Viral Vaccines; D014774:Virulence
D020413:3' Untranslated Regions; C096041:NS5 protein, flavivirus; D014613:Vaccines, Attenuated; D014759:Viral Envelope Proteins; D017361:Viral Nonstructural Proteins; D014765:Viral Vaccines