Cucumber mosaic virus (CMV) and Peanut stunt virus (PSV) each have genomes consisting of three single-stranded RNA molecules: RNA 1, 2 and 3. RNAs 1 and 2 encode the 1a and 2a proteins, respectively, which are necessary for replication of the viral genome. Although RNA 3 is exchangeable between CMV and PSV, exchange of RNA 1 and 2 between the two viruses has been unsuccessful. In this study, reassortants containing PSV RNA 1 and CMV RNA 2 together with RNA 3 of CMV or PSV were shown to be able to replicate their genomic RNA, but not to transcribe subgenomic RNA 4 in tobacco protoplasts. Conversely, the reassortant consisting of CMV RNA 1 and PSV RNA 2 together with RNA 3 of CMV or PSV could not replicate. Subsequently, a yeast two-hybrid system was used to analyse the in vivo interaction between the 1a and 2a proteins. The C-terminal half of PSV-1a protein interacted with the N-terminal region of 2a protein of both PSV and CMV, but the C-terminal half of CMV-1a and the N-terminal region of PSV-2a did not interact. These results suggest that RNA replication in the interspecific reassortant between CMV and PSV requires compatibility between the C-terminal half of the 1a protein and the N-terminal region of the 2a protein, and this compatibility is insufficient for transcription of subgenomic RNA 4. INTRODUCTIONCucumber mosaic virus (CMV) is one of the most important pathogens of many crops, and Peanut stunt virus (PSV) is also an economically important pathogen of legumes worldwide. CMV and PSV are taxonomically related virus species, as shown serologically and by nucleic acid hybridization. They are members of the genus Cucumovirus, together with Tomato aspermy virus (TAV), in the family Bromoviridae, which belongs to the alphavirus-like superfamily (Goldbach, 1987;Koonin & Dolja, 1993). CMV strains are classified into subgroups IA, IB and II (reviewed in Palukaitis et al., 1992;Roossinck et al., 1999). PSV isolates are also classified into two distinct subgroups (Hu et al., 1997).Cucumoviruses have tripartite genomes that consist of three positive-sense, single-stranded RNA molecules, which are designated RNA 1 to 3 in decreasing order of molecular mass. RNA 1 and 2 encode the 1a and 2a proteins, respectively, both of which are necessary for virus replication (Nitta et al., 1988;Hayes & Buck, 1990). RNA 3 encodes the 3a protein, which is involved in virus movement (Suzuki et al., 1991;Canto et al., 1997;Kaplan et al., 1997). RNA 4, which is transcribed from the negative strand of RNA 3, serves as a messenger RNA for the viral coat protein (CP). CP is involved in symptom determination in several plants (Shintaku et al., 1992;Takahashi & Ehara, 1993;Suzuki et al., 1995;Takeshita et al., 1998Takeshita et al., , 2001. Another subgenomic RNA, RNA 4A, which is transcribed from RNA2, encodes the 2b protein, which is not necessary for replication (Ding et al., 1994(Ding et al., , 1995. The RNA 4A of subgroup I CMV was reported to accumulate to a very low level compared with that of subgroup II CMV and TAV (Shi et al., ...

Background: Krill, which morphologically resembles small shrimp, represents small ocean crustaceans and has been used for human consumption in Japan and some other countries. The major allergen in crustaceans has been reported to be tropomyosin, but the allergenicity of krill tropomyosin remains uncertain. Methods: Amino acid sequences of tropomyosin in two species of krill (Euphausia superba and E. pacifica) were deduced. Recombinant krill tropomyosins were produced in Escherichiacoli using a pCold IV vector system, and the cross-reactivity of shrimp allergy-related IgE to the recombinant tropomyosins and several animal protein extracts was assessed by immunoblotting. Results: The deduced amino acid sequences of the E. superba and E. pacifica tropomyosins (designated as Eup s 1 and Eup p 1, respectively) were 284 residues and showed significant homology to those of shrimp, lobster and crab tropomyosins. Shrimp allergy-related IgE reacted to approximately 38-kDa protein bands in krill (E. superba), shrimp, lobster and crab protein extracts but did not react to protein extracts from either mollusks or vertebrates. Furthermore, the IgE recognized rEup s 1 and rEup p 1 as 38-kDa protein bands, and absorption of the IgE with rEup s 1 removed IgE reactivity to recombinant tropomyosins and protein extracts from krill and shrimp. Conclusions: Krill tropomyosins included highly homologous sequences to previously reported IgE-binding epitopes in Pen a 1 (tropomyosin of Penaeus aztecus). The cross-reactivity in shrimp allergy-related IgE binding among krill, shrimp, lobster and crab tropomyosins was revealed. These observations suggest the potential allergenicity of krill tropomyosin.

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