Molecular mechanism on the replication of Bombyx densovirus

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Bombyx mori denso nucleosis virus (Yamanashi isolate ; BmDNV-2) is a small spherical virus with a bi-partite genome. In this study, to elucidate the nature of BmDNV-2, the viral DNA replication mechanism, genome organization and function of viral proteins were investigated. Analysis of the replicative intermediates (RI) of the viral DNA suggested the self-priming and hairpin-transfer model for parvovirus replication could not be applied to the replication of BmDNV-2. Nucleotide sequencing studies of the genomic DNAs showed that, unlike BmDNV-1 and the other parvoviruses the BmDNV-2 terminal sequences did not contained the large palindromic sequence which could form a stable hairpin structure. This was confirmed by the secondary structure prediction using a computer analyzes program. These results also suggested that the BmDNV-2 had a unique replication mechanisms other than the self-priming and hairpin-transfer mechanism.Furthermore, the sequence analyzes elucidated that the BmDNV-2 ge … More nome contained 6 major open reading frames (ORFs), 4 ORFs in VD1 and 2in VD2. Immunochemical studies demonstrated that the major four viral structural proteins (VP1,2,3 and 4) were encoded in the ORF2 of VD1. Followingly, the functions of the nonstructural proteins (NSPs) were investigated by transient expression assay using the luciferase as a reporter. The NSPs, p37 and p14 which were encoded in ORF3 and4 of VD1, respectively, transactivated the tentative promoter sequence for the major structural protein gene, suggesting that these proteins were concerned in the regulation of the expression fo structural proteins. In addition, p27 which was an NSP encoded in VD2 could transactivate all of the viral promoters implying that p27 is a key regulatory protein in the BmDNV-2 replication.In conclusion, this study elucidated the genome structure and the genome organization of the BmDNV-2. The results revealed that the BmDNV-2 is a new type of single-stranded DNA virus with a unique replication mechanism which was different from those of parvoviruses. Furthermore, the functional analyzes of the viral proteins suggested that the viral gene expression was regulated in the complicated manner by the proteins encoded in viral DNAs. And, p27 will be a key regulatory protein in the replication of the BmDNV-2 and may be one of the factor concerning in the determination of the host specificity. Less