Expression of the insect parvovirus GmDNV in vivo: the structural and nonstructural proteins are encoded by opposite DNA strands

Characterization of the promoter elements and transcription profile of Periplaneta fuliginosa densovirus nonstructural genes

Periplaneta fuliginosa Densovirus (PfDNV), an autonomous invertebrate parvovirus that infects the cockroach, is unusual in that alternative splicing is involved in the structural gene expression. The expression strategy for nonstructural (NS) genes has yet not been reported. Northern blot analysis of cockroach larvae infected with PfDNV revealed two transcripts for the NS genes, one of 2.6 kb, and the other of 1.9 kb. The two transcripts were shown to begin at a common initiator consensus sequence, CAGT, located in the terminus of ITR. The 1.9 kb transcript was produced by splicing out the ns3 gene from the 2.6 kb transcript. To understand the mechanism of transcriptional regulation of NS genes, the 5'-flanking sequence of ns3 gene (325 bp), which encompasses the region from the 5'-terminus of the viral genome to the initiator ATG codon of the ns3 gene, was cloned and fused to a luciferase reporter gene. The luciferase reporter assay showed that this sequence possessed promoter activity in Sf9, Ld652, Tn368, and S2 cell lines. Subsequent promoter deletion analysis showed that the promoter exhibited TATA-dependent and TATA-independent transcriptional activities. Moreover, we found that the promoter activity of the 325-bp fragment in S2 cells could be enhanced significantly by co-transfection of the nonstructural protein NS1 and that the NS1 binding element, (CAC)(4) repeat, mediated the promoter activity activated by NS1 protein.

Organization and expression strategy of the ambisense genome of densonucleosis virus of Galleria mellonella

The expression strategy of parvoviruses of the Densovirus genus has as yet not been reported. Clones were obtained from the densonucleosis virus of Galleria mellonella (GmDNV) that yielded infectious virus upon transfection into LD652 cells. Its genome was found to be the longest (6,039 nucleotides [nt]), with the largest inverted terminal repeats (ITRs) (550 nt) among all parvoviruses. The distal 136 nt could be folded into hairpins with flop or flip sequence orientations. In contrast to vertebrate parvoviruses, the gene cassettes for the nonstructural (NS) and structural (VP) proteins were found on the 5' halves of the opposite strands. The transcripts for both cassettes started 23 nt downstream of the ITRs. The TATA boxes, as well as all upstream promoter elements, were localized in the ITRs and, therefore, identical for the NS and VP transcripts. These transcripts overlapped for 60 nt at the 3' ends (antisense RNAs) at 50 m.u. The NS cassette consisted of three genes of which NS2 was contained completely within NS1 but from a different reading frame. Most of the NS transcripts were spliced to remove the upstream NS3, allowing leaky scanning translation of NS1 and NS2, similar to the genes of RNA-6 of influenza B virus. NS3 could be translated from the unspliced transcript. The VP transcript was not spliced and generated four VPs by a leaky scanning mechanism. The 5'-untranslated region of the VP transcript was only 5 nt long. Despite the transcription and translation strategies being radically different from those of vertebrate parvoviruses, the capsid was found to have phospholipase A(2) activity, a feature thus far unique for parvoviruses.

A new virus infecting Myzus persicae has a genome organization similar to the species of the genus Densovirus

The genomic sequence of a new icosahedral DNA virus infecting Myzus persicae has been determined. Analysis of 5499 nt of the viral genome revealed five open reading frames (ORFs) evenly distributed in the 5' half of both DNA strands. Three ORFs (ORF1-3) share the same strand, while two other ORFs (ORF4 and ORF5) are detected in the complementary sequence. The overall genomic organization is similar to that of species from the genus DENSOVIRUS: ORFs 1-3 most likely encode the non-structural proteins, since their putative products contain conserved replication motifs, NTP-binding domains and helicase domains similar to those found in the NS-1 protein of parvoviruses. The deduced amino acid sequences from ORFs 4 and 5 show sequence similarities with the structural proteins of the members of the genus DENSOVIRUS: These data indicate that this virus is a new species of the genus Densovirus in the family PARVOVIRIDAE: The virus was tentatively named Myzus persicae densovirus.