Biochemical characterization of Periplaneta fuliginosa densovirus non-structural protein NS1

An investigation into the effects of infection and ORF expression patterns of the Indian bidensovirus isolate (BmBDV) infecting the silkworm Bombyx mori

The Indian isolate of Bombyx mori bidensovirus (BmBDV) is a bipartite virus that comprises of a segmented, non-homologous, two linear single-strands of DNA molecules (VD1 and VD2). It is one of the causative agents of the fatal silkworm disease 'Flacherie' that causes severe crop loss for the sericulture farmers. Genome analyses of the Indian isolate of BmBDV revealed that it consists of 6 putative ORFs similar to the Japanese and Chinese isolates. VD1 consists of 4 ORFs while VD2 has 2 ORFs that code for 4 non- structural (NS) and 2 structural (VP) proteins, in total. In this study, we investigated, in detail, the impact of BmBDV pathogenesis on growth and development of the silkworm Bombyx mori, at different developmental stages. Mortality rate and weight uptake analyses were also performed on newly ecdysed 4th instar larvae. BmBDV infection was not found to be developmental stage specific and it occurred at all stages. Onset of mortality took place 8 days post infection (dpi) and 100% mortality occurred at 11 dpi. The infected larvae showed a significant difference in weight uptake wherein from 7 dpi the larvae stopped gaining weight and from 8th dpi started demonstrating the typical symptoms of flacherie. Further, the expression pattern of the 6 viral ORFs were also investigated in the newly ecdysed 4th instar BmBDV infected silkworms. Among all the six ORFs, VD2 ORF 1 and 2 revealed the highest transcript numbers, which was followed by VD1 ORF 4 that encodes for the viral DNA polymerase enzyme. This was the first ever attempt to understand the pathogenesis and the expression pattern of all the six ORF transcripts of the Indian isolate of BmBDV.

Evidence for densovirus integrations into tapeworm genomes

BACKGROUND

Tapeworms lack a canonical piRNA-pathway, raising the question of how they can silence existing mobile genetic elements (MGE). Investigation towards the underlying mechanisms requires information on tapeworm transposons which is, however, presently scarce.

METHODS

The presence of densovirus-related sequences in tapeworm genomes was studied by bioinformatic approaches. Available RNA-Seq datasets were mapped against the Echinococcus multilocularis genome to calculate expression levels of densovirus-related genes. Transcription of densovirus loci was further analyzed by sequencing and RT-qPCR.

RESULTS

We herein provide evidence for the presence of densovirus-related elements in a variety of tapeworm genomes. In the high-quality genome of E. multilocularis we identified more than 20 individual densovirus integration loci which contain the information for non-structural and structural virus proteins. The majority of densovirus loci are present as head-to-tail concatemers in isolated repeat containing regions of the genome. In some cases, unique densovirus loci have integrated close to histone gene clusters. We show that some of the densovirus loci of E. multilocularis are actively transcribed, whereas the majority are transcriptionally silent. RT-qPCR data further indicate that densovirus expression mainly occurs in the E. multilocularis stem cell population, which probably forms the germline of this organism. Sequences similar to the non-structural densovirus genes present in E. multilocularis were also identified in the genomes of E. canadensis, E. granulosus, Hydatigera taeniaeformis, Hymenolepis diminuta, Hymenolepis microstoma, Hymenolepis nana, Taenia asiatica, Taenia multiceps, Taenia saginata and Taenia solium.

CONCLUSIONS

Our data indicate that densovirus integration has occurred in many tapeworm species. This is the first report on widespread integration of DNA viruses into cestode genomes. Since only few densovirus integration sites were transcriptionally active in E. multilocularis, our data are relevant for future studies into gene silencing mechanisms in tapeworms. Furthermore, they indicate that densovirus-based vectors might be suitable tools for genetic manipulation of cestodes.

Linear Lepidopteran ambidensovirus 1 sequences drive random integration of a reporter gene in transfected Spodoptera frugiperda cells

BACKGROUND

The Lepidopteran ambidensovirus 1 isolated from Junonia coenia (hereafter JcDV) is an invertebrate parvovirus considered as a viral transduction vector as well as a potential tool for the biological control of insect pests. Previous works showed that JcDV-based circular plasmids experimentally integrate into insect cells genomic DNA.

METHODS

In order to approach the natural conditions of infection and possible integration, we generated linear JcDV-gfp based molecules which were transfected into non permissive Spodoptera frugiperda (Sf9) cultured cells. Cells were monitored for the expression of green fluorescent protein (GFP) and DNA was analyzed for integration of transduced viral sequences. Non-structural protein modulation of the VP-gene cassette promoter activity was additionally assayed.

RESULTS

We show that linear JcDV-derived molecules are capable of long term genomic integration and sustained transgene expression in Sf9 cells. As expected, only the deletion of both inverted terminal repeats (ITR) or the polyadenylation signals of NS and VP genes dramatically impairs the global transduction/expression efficiency. However, all the integrated viral sequences we characterized appear "scrambled" whatever the viral content of the transfected vector. Despite a strong GFP expression, we were unable to recover any full sequence of the original constructs and found rearranged viral and non-viral sequences as well. Cellular flanking sequences were identified as non-coding ones. On the other hand, the kinetics of GFP expression over time led us to investigate the apparent down-regulation by non-structural proteins of the VP-gene cassette promoter.

CONCLUSION

Altogether, our results show that JcDV-derived sequences included in linear DNA molecules are able to drive efficiently the integration and expression of a foreign gene into the genome of insect cells, whatever their composition, provided that at least one ITR is present. However, the transfected sequences were extensively rearranged with cellular DNA during or after random integration in the host cell genome. Lastly, the non-structural proteins seem to participate in the regulation of p9 promoter activity rather than to the integration of viral sequences.

DNA Binding and Cleavage by the Human Parvovirus B19 NS1 Nuclease Domain

Infection with human parvovirus B19 (B19V) has been associated with a myriad of illnesses, including erythema infectiosum (Fifth disease), hydrops fetalis, arthropathy, hepatitis, and cardiomyopathy, and also possibly the triggering of any number of different autoimmune diseases. B19V NS1 is a multidomain protein that plays a critical role in viral replication, with predicted nuclease, helicase, and gene transactivation activities. Herein, we investigate the biochemical activities of the nuclease domain (residues 2-176) of B19V NS1 (NS1-nuc) in sequence-specific DNA binding of the viral origin of replication sequences, as well as those of promoter sequences, including the viral p6 and the human p21, TNFα, and IL-6 promoters previously identified in NS1-dependent transcriptional transactivation. NS1-nuc was found to bind with high cooperativity and with multiple (five to seven) copies to the NS1 binding elements (NSBE) found in the viral origin of replication and the overlapping viral p6 promoter DNA sequence. NS1-nuc was also found to bind cooperatively with at least three copies to the GC-rich Sp1 binding sites of the human p21 gene promoter. Only weak or nonspecific binding of NS1-nuc to the segments of the TNFα and IL-6 promoters was found. Cleavage of DNA by NS1-nuc occurred at the expected viral sequence (the terminal resolution site), but only in single-stranded DNA, and NS1-nuc was found to covalently attach to the 5' end of the DNA at the cleavage site. Off-target cleavage by NS1-nuc was also identified.

Regulation of BmBDV NS1 by phosphorylation: Impact of mutagenesis at consensus phosphorylation sites on ATPase activity and cytopathic effects

Bombyx mori bidensovirus (BmBDV) is a single-stranded DNA virus belonging to the Bidensovirus genus, Bidnaviridae family. Previous studies showed that parvovirus nonstructural protein 1 (NS1) contains endonuclease, helicase, and ATPase activities and that these activities are regulated by serine/threonine phosphorylation. We have reported that residue Thr-184 site of BmBDV NS1 is phosphorylated, and that residues of Thr-181 and Thr-191 are potentially phosphorylated. However, whether phosphorylation affects BmBDV NS1 activities remains unclear. In this study, the substitution of threonine with Glycine at positions 181, 184 and 191 of BmBDV NS1 reduced its ATPase activity. After wild-type NS1 was treated with calf intestinal alkaline phosphatase (CIP), ATPase activity decreased significantly. Moreover, silkworms that were injected with recombinant viruses carrying these NS1 mutations exhibited significant increases in the median lethal time to death compared with silkworms that were injected with a virus that expressed wild-type NS1. In conclusion, these results showed that the ATPase activity and virulence of BmBDV NS1 are regulated via phosphorylation.

The identification and characterization of nucleic acid chaperone activity of human enterovirus 71 nonstructural protein 3AB

Human enterovirus 71 (EV71) belongs to the genus Enterovirus in the family Picornaviridae and has been recognized as one of the most important pathogens that cause emerging infectious disease. Despite of the importance of EV71, the nonstructural protein 3AB from this virus is little understood for its function during EV71 replication. Here we expressed EV71 3AB protein as recombinant protein in a eukaryotic expression system and uncovered that this protein possesses a nucleic acid helix-destabilizing and strand annealing acceleration activity in a dose-dependent manner, indicating that EV71 3AB is a nucleic acid chaperone protein. Moreover, we characterized the RNA chaperone activity of EV71 3AB, and revealed that divalent metal ions, such as Mg²⁺ and Zn²⁺, were able to inhibit the RNA helix-destabilizing activity of 3AB to different extents. Moreover, we determined that 3B plus the last 7 amino acids at the C-terminal of 3A (termed 3B+7) possess the RNA chaperone activity, and five amino acids, i.e. Lys-80, Phe-82, Phe-85, Tyr-89, and Arg-103, are critical and probably the active sites of 3AB for its RNA chaperone activity. This report reveals that EV71 3AB displays an RNA chaperone activity, adds a new member to the growing list of virus-encoded RNA chaperones, and provides novel knowledge about the virology of EV71.

The nonstructural protein 2C of a Picorna-like virus displays nucleic acid helix destabilizing activity that can be functionally separated from its ATPase activity

Picorna-like viruses in the Picornavirales order are a large group of positive-strand RNA viruses that include numerous important pathogens for plants, insects, and humans. In these viruses, nonstructural protein 2C is one of the most conserved proteins and contains ATPase activity and putative RNA helicase activity. Here we expressed 2C protein of Ectropis obliqua picorna-like virus (EoV; genus Iflavirus, family Iflaviridae, order Picornavirales) in a eukaryotic expression system and determined that EoV 2C displays ATP-independent nucleic acid helix destabilizing and strand annealing acceleration activity in a concentration-dependent manner, indicating that this picornaviral 2C is more like an RNA chaperone than like the previously predicted RNA helicase. Our further characterization of EoV 2C revealed that divalent metal ions, such as Mg(2+) and Zn(2+), inhibit 2C-mediated helix destabilization to different extents. Moreover, we determined that EoV 2C also contains ATPase activity like that of other picornaviral 2C proteins and further assessed the functional relevance between its RNA chaperone-like and ATPase activities using mutational analysis as well as their responses to Mg(2+). Our data show that, when one of the two 2C activities was dramatically inhibited or almost abolished, the other activity could remain intact, showing that the RNA chaperone-like and ATPase activities of EoV 2C can be functionally separated. This report reveals that a picorna-like virus 2C protein displays RNA helix destabilizing and strand annealing acceleration activity, which may be critical for picornaviral replication and pathogenesis, and should foster our understanding of picorna-like viruses and viral RNA chaperones.

Periplaneta fuliginosa densovirus nonstructural protein NS1 contains an endonuclease activity that is regulated by its phosphorylation

Periplaneta fuliginosa densovirus (PfDNV) is a single-stranded DNA virus, belonging to Densovirinae subfamily, Parvoviridae family. Parvovirus nonstructural protein 1 (NS1) contains various activities required for parvoviral DNA replication, like endonuclease, helicase and ATPase, which are regulated by serine/threonine phosphorylation. However, for PfDNV, NS1 endonuclease activity has not been determined. Moreover, for densoviruses, whether NS1 is phosphorylated, and if so, phosphorylation pattern and impact on NS1 activities have not been investigated. Here, we demonstrated that PfDNV NS1 possesses endonuclease activity, covalently attaches to 5'-end of nicking site, and includes an active-site tyrosine (Y178). Moreover, using different phosphatases, we uncovered that both serine/threonine and tyrosine phosphorylations are critical for NS1 endonuclease and helicase activities. Further mass-spec and mutational analyses revealed that Y345 is phosphorylated and functions as a critical regulatory site for NS1 activities. This study should foster our understanding of NS1 activities and regulations in PfDNV and other densoviruses.

Identification and characterization of RNA duplex unwinding and ATPase activities of an alphatetravirus superfamily 1 helicase

Dendrolimus punctatus tetravirus (DpTV) belongs to the genus omegatetravirus of the Alphatetraviridae family. Sequence analysis predicts that DpTV replicase contains a putative helicase domain (Hel). However, the helicase activity in alphatetraviruses has never been formally determined. In this study, we determined that DpTV Hel is a functional RNA helicase belonging to superfamily-1 helicase with 5′–3′ dsRNA unwinding directionality. Further characterization determined the length requirement of the 5′ single-stranded tail on the RNA template and the optimal reaction conditions for the unwinding activity of DpTV Hel. Moreover, DpTV Hel also contains NTPase activity. The ATPase activity of DpTV Hel could be significantly stimulated by dsRNA, and dsRNA could partially rescue the ATPase activity abolishment caused by mutations. Our study is the first to identify an alphatetravirus RNA helicase and further characterize its dsRNA unwinding and NTPase activities in detail and should foster our understanding of DpTV and other alphatetraviruses.

Characterization of the promoter elements of Bombyx mori bidensovirus nonstructural gene 1

Bombyx mori Bidensovirus (BmBDV), a bipartite virus possesses two single-stranded linear DNAs (VD1 and VD2) and shows high pathogenic ability to Bombyx mori. Previous research found that the genes of nonstructural protein ns1 and ns2 were in the same transcript. To investigate the mechanism of transcriptional regulation of ns1 and ns2 genes, the 5'-flanking sequence (289 nt) of ns1 gene, encompasses the regions of the common terminal sequence (CTS) and the predicted P5 promoter from the 5'-terminus of the viral genome to the transcription initiation site of the ns1 gene was cloned and fused to the upstream of the luciferase reporter gene. The luciferase reporter assay showed that the 53 nt CTS of VD1 and VD2 can downregulate the activity of P5 by 13.3 %. The comparison in different cell lines showed that P5 possessed high promoter activity in BmN and Hi5 cell lines. Interestingly, P5 also had high activity in Hela cells, a kind of cancer cell of human. Subsequent truncated promoter analysis showed that the 31 nt (-236 to -206 nt) sequence is very important to P5 for the activity down to 36.5 % after deletion of it. While the activity also remained 26.5 % after the deletion of the TATA box, suggesting that the promoter is TATA independent. Moreover, in order to further understand the activity intensity of P5, a comparison with other three promoters, B. mori actin3 (Bm-actin3), B. mori nuclear polyhedrosis virus (BmNPV) immediate early 1 gene promoter (BmNPV-ie-1), and a synthetic promoter (3xP3) was carried out, the result indicated that the activity of P5 was weaker than that of anyone of them.

Expression strategy of densonucleosis virus from the German cockroach, Blattella germanica

Blattella germanica densovirus (BgDNV) is an autonomous parvovirus that infects the German cockroach. BgDNV possesses three mRNAs for NS proteins, two of which are splice variants of the unspliced transcript. The unspliced variant encodes open reading frame 5 (ORF5) (NS3), while NSspl1 encodes ORF3 (NS1) and ORF4 (NS2) and NSspl2 encodes the C-proximal half of NS1. BgDNV possesses three VP transcripts, one of which (VP) is unspliced, while the other two (VPspl1 and VPspl2) are generated by alternative splicing. The unspliced VP transcript contains both ORF1 and ORF2, while in VPspl1, ORF1 and ORF2 are joined in frame. The transcription of NS genes begins at an earlier stage of the virus life cycle than the transcription of VP genes. NS and VP transcripts overlap by 48 nucleotides (nt). BgDNV is characterized by two additional NS transcripts overlapping by more than 1,650 nt with VP-coding transcripts. Four different bands (97, 85, 80, and 57 kDa) corresponding to three BgDNV capsid proteins were detected on SDS-PAGE. Mass spectrometry analysis showed that the amino acid composition of the 85-kDa and 80-kDa proteins is the same. Moreover, both of these proteins are ubiquitinated. The BgDNV PLA(2) domain, which is critical for cellular uptake of the virus, is located in ORF2 and is present only in VP1. In contrast to all of the parvoviruses studied in this respect, VP2 has a unique N terminus that is not contained within VP1 and VP3. In situ recognition with NS1- and VP-specific antibodies revealed an uneven pattern of NS1 expression resembling a halo within the nuclear membrane.

RNA binding by a novel helical fold of b2 protein from wuhan nodavirus mediates the suppression of RNA interference and promotes b2 dimerization

Wuhan nodavirus (WhNV) is a newly identified member of the Nodaviridae family with a bipartite genome of positive-sense RNAs. A nonstructural protein encoded by subgenomic RNA3 of nodaviruses, B2, serves as a potent RNA silencing suppressor (RSS) by sequestering RNA duplexes. We have previously demonstrated that WhNV B2 blocks RNA silencing in cultured Drosophila cells. However, the molecular mechanism by which WhNV B2 functions remains unknown. Here, we successfully established an RNA silencing system in cells derived from Pieris rapae, a natural host of WhNV, by introducing into these cells double-stranded RNA (dsRNA)-expressing plasmids or chemically synthesized small interfering RNAs (siRNAs). Using this system, we revealed that the WhNV B2 protein inhibited Dicer-mediated dsRNA cleavage and the incorporation of siRNA into the RNA-induced silencing complex (RISC) by sequestering dsRNA and siRNA. Based on the modeled B2 3-dimensional structure, serial single alanine replacement mutations and N-terminal deletion analyses showed that the RNA-binding domain of B2 is formed by its helices α2 and α3, while helix α1 mediates B2 dimerization. Furthermore, positive feedback between RNA binding and B2 dimerization was uncovered by gel shift assay and far-Western blotting, revealing that B2 dimerization is required for its binding to RNA, whereas RNA binding to B2 in turn promotes its dimerization. All together, our findings uncovered a novel RNA-binding mode of WhNV B2 and provided evidence that the promotion effect of RNA binding on dimerization exists in a viral RSS protein.

A recombinant AeDNA containing the insect-specific toxin, BmK IT1, displayed an increasing pathogenicity on Aedes albopictus

The Aedes aegypti densovirus (AeDNV) has previously shown potential in mosquito control. To improve its efficacy as a biopesticide, the gene for an excitatory insect-specific toxin from Buthus martensii Karsch (BmK IT1) was inserted into the AeDNV genome and cloned into pUCA plasmid. The coding sequence for green fluorescent protein was ligated to the C-terminus of the BmK IT1 gene as a screening marker. Recombinant and helper plasmids were cotransfected into C6/36 cells; wild-type viruses were the controls. The recombinant viruses were identified and quantified by real-time polymerase chain reaction and exposed to Ae. albopictus larvae for the evaluation of its bioinsecticidal activity. LT(50) and LD(50) bioassays showed that the recombinant AeDNV had stronger and faster pathogenic effects on Ae. albopictus than the wild-type virus. This is the first report on the recombinant AeDNA containing the insect-specific toxin, BmK IT1, which may be used to develop a novel type of insecticide.

Characterization of Bombyx mori parvo-like virus non-structural protein NS1

NS1 gene of Bombyx mori parvo-like virus (China Zhenjiang isolate, BmDNV-Z) codes a predicted 316-amino acid protein, but its function remains unknown. Results of the current study showed that purified recombinant 6 x His-NS1 protein possesses ATP binding, ATPase, DNA binding, and helicase activities. Only one protein was captured in infected Bombyx mori midgut cells against NS1 target protein by employing co-immunoprecipitation, which was identified to be a viral protein by mass spectrometry. The NS1-interacting protein is encoded by BmDNV-Z ORF4 and its molecular is about 100 kD. Analysis of His pull-down confirmed that binding of identified viral protein to purified recombinant 6 x His-NS1 protein in vitro. Taken together, our results indicated that BmDNV-Z NS1 was a multifunctional protein, which may be involved with virus replication.

The nuclear localization signal of the NS1 protein is essential for Periplaneta fuliginosa densovirus infection

The regulatory protein NS1 is a key molecule in life cycle of Periplaneta fuliginosa densovirus (PfDNV). When we ectopically expressed the PfDNV NS1 protein in non-P. fuliginosa insect cells, the NS1 protein could not enter the nucleus and remained in the cytosol. However, the NS1 was localized to both the cytosol and nucleus of cockroach hemocyte cells. So we investigated the abilities of the potential nuclear localization signal (NLS) of P. fuliginosa Densovirus non-structural protein 1 (NS1) to translocate NS1 and a carrier protein to the nucleus following transfection into insect cells. Possible nuclear localization sequences were chosen from the NS1 on the basis of the presence of basic residues, which is a common theme in most of the previously identified targeting peptides. Nuclear localization activity was found within the residues 252-257 (RRRRRR) of the NS1, while replacement of a single arginine in this region with glycine abolished it. The targeting activity was enhanced with the arginine residues added.

Expression of non-structural protein NS3 gene of Bombyx mori densovirus (China isolate)

The invertebrate parvovirus Bombyx mori Densonucleosis Virus type 3 (China isolate), named BmDNV-3, is a kind of bidensovirus. It is a new type of virus with unique replication mechanisms. To investigate the effects of the NS3 gene during viral DNA replication, a pair of primers was designed for amplifying NS3 gene of Bombyx mori densovirus (China isolate). Gene NS3 amplified was cloned into a prokaryotic expression vector pET-30a and the donor plasmid pFastBacHTe, respectively. The NS3 protein was expressed in Escherichia coli BL21. The pFastBacHTe-NS3 was transformed to E. coli DH10Bac. The recombinant bacmid baculoviruses (rBacmid-EGFP-NS3) isolated from the white colonies were transfected into BmN-4 cells using a transfection reagent. BmN-4 cells were infected with recombinant virus to express fusion proteins. The expression of fusion protein around 30 kDa in E. coli BL21 was identified by SDS-PAGE, Western blotting, and mass spectrometry. The expressed NS3 protein by B. mori nucleopolyhedrovirus bacmid system was confirmed by Western blotting using an anti-NS3 polyclonal antibody. And about 45 kDa protein was found. The expressed fusion protein was smaller than the expected size of EGFP-NS3, 55 kDa. Western blotting analysis indicated that EGFP-NS3 protein was expressed in infected larvae with smaller molecular size.

Non-structural proteins of Periplaneta fuliginosa densovirus inhibit cellular gene expression and induce necrosis in Sf9 cell cultures

The non-structural protein NS1 of Periplaneta fuliginosa densovirus (PfDNV) is a multifunctional protein that has previously been shown to possess ATP-binding, ATPase, site-specific DNA-binding, helicase, and transcription activation activities. We report here an investigation of the cytopathogenicity of this viral non-structural (NS) protein, as well as other two NSs, NS2, and NS3, in cultured insect cells. The expression of NS1 alone potently inhibited cellular gene expression, whereas NS2 and NS3 did not produce a similar effect. The inhibition of gene expression by NS1 was confirmed to be specific and not a simple manifestation of toxicity. For example, NS1 inhibited expression of several reporter genes under the control of different RNA polymerase II promoters, whereas it did not inhibit expression from a T7 RNA polymerase promoter construct. Mapping analysis identified the carboxy-terminal peptide of this protein as the region important for the inhibition of cellular gene expression, suggesting that this inhibition is independent of its DNA-binding activity. Next, the mutagenesis assay showed that ATP-binding was essential for the unique function of this protein. Furthermore, we found that NS2 and NS3 cooperatively enhanced the NS1-induced transcription inhibition. Co-expression of all the three NS proteins in Sf9 cells also led to necrotic cell death by ATP depletion.

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.

The densovirus of Periplaneta fuliginosa (PfDNV) as an insect vector for persistent foreign gene expression in vivo

An infectious clone of the Periplaneta fuliginosa densovirus (PfDNV) has been constructed and the PfDNV genome can rescue from the plasmid and replicate as the wild-type virus in nymphs of P. fuliginosa. To investigate the ability of the cloned PfDNV genome to be used as a stable and persistent expression vector, we constructed seven recombinant plasmids in which the GFP reporter gene was inserted into the genome of PfDNV. When these recombinant constructs were transfected into hosts, the GFP was expressed efficiently in every clone. Southern blot analysis revealed that recombinant plasmids had integrated into host genome. Infectious recombinant virions could be produced from plasmids in which the GFP gene was downstream of and in frame with the NS3 and NS1 coding regions. These results indicate that PfDNV genome can be used as an insect vector for the transfer and persistent expression of an exogenous gene.