| Budget Amount *help |
¥3,920,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥420,000)
Fiscal Year 2007: ¥1,820,000 (Direct Cost: ¥1,400,000、Indirect Cost: ¥420,000)
Fiscal Year 2006: ¥2,100,000 (Direct Cost: ¥2,100,000)
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| Research Abstract |
Betanodaviruses, the causal agents of viral nervous necrosis in marine fish, have bipartite positive-sense RNA genomes. The larger genomic segment RNA1 (3.1 kb) encodes an RNA-dependent RNA polymerase (protein A) and the smaller genomic segment RNA2 (1A kb) Codes for the coat protein The viruses can be classified into four genotypes, designated SJNNV, RGNNV, TPNNV and BFNNV, based on similarities in the partial RNA2 sequence. The optimal temperatures for multiplication of these viruses were 20-25℃ (SJNNV), 25-30℃ (RGNNV), 20℃ (TPNNV) and 15-20℃ (BFNNV). However, little is known about the mechanisms underlying temperature sensitivities of these viruses. In order to know the segment(s) that control temperature sensitivity, we first constructed two reassortants between SJNNV and RGNNV. Multiplication of these reassortantsandSINNVinculturedfishcellsat30℃ was strongly inhibited compared with those of RONNY. The viral multiplication levels were well correlated with those of viral RNA replication. These results indicate that both. RNA1 and RNA2 control temperature sensitivities of betanodaviruses , via modulating RNA replication or earlier virus multiplication processes. Second, to identify an RNA1 region(s) that confers temperature sensitivities, we constructed 10 mutated viruses having chimeric RNA1 segments between SJNNV and RGNNV. Evaluation of temperature sensitivities in these chimeric viruses showed that the 5' terminus of the protein A-coding region in RNA1 strongly control temperature sensitivities The ,N-terminal portion of protein A is known to serve a mitochondrial targeting signal rather than function as an enzymatic domain.
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