Terminal structure of a Densovirus implies a hairpin transfer replication which is similar to the model for AAV

Resistance mechanism of Nid-1, a dominant non-susceptibility gene, against Bombyx mori densovirus 1 infection

Bombyx mori densovirus 1 (BmDV1) is a pathogen that causes flacherie disease in mulberry silkworms (B. mori). The absolute resistance (non-susceptibility) to BmDV1 of certain silkworm strains is determined independently by two genes, nsd-1 and Nid-1. Previously, we investigated the expression of viral transcript in virus-inoculated silkworms carrying different nsd-1 and Nid-1 genotypes, and observed that nsd-1 and Nid-1 expression blocked the early and late steps of BmDV1 infection, respectively. In addition, we found that nsd-1 encoded a Bombyx-specific mucin-like membrane protein only present on the surface of the midgut, where BmDV1 could infect. In this study, we dissected the resistance mechanism by Nid-1 against BmDV1 infection by investigating the sequential changes in the accumulation of viral DNA, transcripts, and proteins derived from BmDV1 in susceptible strain (pxj) and Nid-1-carrying resistant strain (No. 908) after inoculation with BmDV1. Genomic PCR results showed that the BmDV1 DNA was detected immediately after the infection in both strains but rapidly decreased in the Nid-1-carrying strain No. 908 compared with the susceptible strain pxj. RT-PCR results also showed that the BmDV1 transcripts of Nid-1-carrying strain No. 908 were rapidly decreased after the infection. Moreover, BmDV1-derived proteins were not detected in No. 908 throughout the infection. These results suggest that Nid-1 expression might inhibit the accumulation of viral DNA and transcripts. As Nid-1 has not been molecularly characterized, its identification will contribute to the elucidation of the interactions between the silkworm and BmDV1.

Complete nucleotide sequence analysis of a Korean strain of hepatopancreatic parvovirus (HPV) from Fenneropenaeus chinensis

Hepatopancreatic parvovirus (HPV) of shrimp is distributed worldwide and the entire genome of Thailand and Indian strains (PmDNV) and one Australian strain (PmergDNV) have now been reported. The complete nucleotide sequence of a HPV strain isolated from the fleshy prawn Fenneropenaeus chinensis in Korea (FcDNV) was determined and compared to previously reported sequences. The entire genome of FcDNV contains 6,336 nucleotides, with 40% G+C content, which is the biggest of the known HPV strains. The HPV genome has three open reading frames (ORFs) with a slight overlap between the first and second ORFs. The three ORFs encode the NS2 and NS1 proteins and VP that consist of 425, 578, and 820 amino acids, respectively. Among the three proteins, the NS1 protein shows the highest sequence similarity to the NS1 protein of other known HPV strains, followed by the NS2 protein and the VP protein. Phylogenetic analyses showed that HPV can be grouped into three genotypes, as previously reported, and FcDNV can be grouped as genotype I, with HPV strains isolated in Madagascar and Tanzania. The nucleotide sequences of the noncoding regions at the 5'- and 3'-ends of the plus-strand genome showed a Y-shaped hairpin structure and simple hairpin structure, respectively.

Molecular cloning and expression of key gene encoding hypothetical DNA polymerase from B. mori parvo-like virus

BmPLV-Z is the abbreviation for Bombyx mori parvo-like virus (China isolate). This is a novel virus with two single-stranded linear DNA molecules, viz., VD1 (6543 bp) and VD2 (6022 bp), which are encapsidated respectively into separate virions. Analysis of the deduced amino acid sequence of VD1-ORF4 indicated the existence of a putative DNA-polymerase with exonuclease activity, possibly involved in the replication of BmPLV-Z. In the present study, a recombinant baculovirus was constructed to express the full length of the protein encoded by the VD1-ORF4 gene (3318 bp). In addition, a 2163-bp fragment amplified from the very same gene was cloned into prokaryotic expression vector pET-30a and expressed in E.coli Rosetta 2 (DE3) pLysS. The expressed fusion protein was employed to immunize New Zealand white rabbits for the production of an antiserum, afterwards used for examining the expression of the protein encoded by VD1-ORF4 gene in Sf-9 cells infected with recombinant baculovirus. Western blot analysis of extracts from thus cells infected revealed a specific band of about 120 kDa, thereby indicating that the full length protein encoded by the VD1-ORF4 gene had been successfully and stably expressed in Sf-9 cells.

Differentially expressed genes in resistant and susceptible Bombyx mori strains infected with a densonucleosis virus

We investigated variations in the gene expression of Bombyx mori following infection with a densonucleosis virus (BmDNV-Z). Two B. mori near-isogenic lines, Jingsong and Jingsong.nsd-Z.NIL, which are highly susceptible and completely resistant to BmDNV-Z, respectively, were used in this study. The infection profiles of BmDNV-Z in the midguts of the B. mori Jingsong and Jingsong.nsd-Z.NIL larvae revealed that the virus invaded the midguts of both of these strains. However, its proliferation was notably inhibited in the midgut of the resistant strain. By using the suppression subtractive hybridization method, three cDNA libraries were constructed to compare BmDNV-Z responsive gene expression between the two silkworm lines. In total, 151 differentially expressed genes were obtained. Real-time qPCR analysis confirmed that 11 genes were significantly up-regulated in the midgut of the Jingsong.nsd-Z.NIL strain following BmDNV-Z infection. Our results imply that these up-regulated genes might be involved in B. mori immune responses against BmDNV infection.

Characterization of a new densovirus infecting the German cockroach, Blattella germanica

A new DNA virus (Parvoviridae: Densovirinae, Densovirus) was isolated and purified from descendants of field-collected German cockroaches, Blattella germanica. Viral DNA and cockroach tissues infected with B. germanica densovirus (BgDNV) were examined by electron microscopy. Virus particles, about 20 nm in diameter, were observed both in the nucleus and in the cytoplasm of infected cells. Virus DNA proved to be a linear molecule of about 1.2 microm in length. BgDNV isolated from infected cockroaches infected successfully and could be maintained in BGE-2, a B. germanica cell line. The complete BgDNV genome was sequenced and analysed. Five open reading frames (ORFs) were detected in the 5335 nt sequence: two ORFS that were on one DNA strand encoded structural capsid proteins (69.7 and 24.8 kDa) and three ORFs that were on the other strand encoded non-structural proteins (60.2, 30.3 and 25.9 kDa). Three putative promoters and polyadenylation signals were identified. Structural analysis of the inverted terminal repeats revealed the presence of extended palindromes. The genome structure of BgDNV was compared with that of other members of the family Parvoviridae; the predicted amino acid sequences were aligned and subjected to phylogenetic analyses.

Biochemical characterization of Periplaneta fuliginosa densovirus non-structural protein NS1

The non-structural (NS) proteins of parvoviruses are involved in essential steps of the viral life cycle. Various biochemical functions, such as ATP binding, ATPase, site-specific DNA binding and nicking, and helicase activities, have been assigned to the protein NS1. Compared with the non-structural proteins of the vertebrate parvoviruses, the NS proteins of the Densovirinae have not been well characterized. Here, we describe the biochemical properties of NS1 of Periplaneta fuliginosa densovirus (PfDNV). We have expressed and purified NS1 using a baculovirus system and analyzed its enzymatic activity. The purified recombinant NS1 protein possesses ATPase- and ATP- or dATP-dependent helicase activity requiring either Mg(2+) or Mn(2+) as a cofactor. The ATPase activity of NS1 can be efficiently stimulated by single-stranded DNA. The ATPase coupled helicase activity was detected on blunt-ended double-stranded oligonucleotide substrate. Using South-Western and Dot-spot assays, we identified a DNA fragment that is recognized specifically by the recombinant NS1 protein. The fragment consists of (CAC)(4) and is located on the hairpin region of the terminal palindrome. The domain for DNA binding was defined to the amino-terminal region (amino acids 1-250). In addition, we found that NS1 can form oligomeric complexes in vivo and in vitro. Mutagenesis analysis showed that ATP binding is necessary for oligomerization. Based on these results, it seems that PfDNV NS1, a multifunctional protein, plays an important role in viral DNA replication comparable to those of vertebrate parvovirus initiator proteins.

Complete nucleotide sequence and genomic organization of hepatopancreatic parvovirus (HPV) of Penaeus monodon

We have determined the genome of hepatopancreatic parvovirus (HPV), a minus, single-stranded DNA virus isolated from infected Penaeus monodon in Thailand. Its genome consisted of 6321 nucleotides, representing three large open reading frames (ORFs) and two non-coding termini. The left (ORF1), mid (ORF2), and right (ORF3) ORFs on the complementary (plus) strand may code for 428, 579, and 818 amino acids, equivalent to 50, 68, and 92 kDa, respectively. The 5' and 3' ends of viral genome contained hairpin-like structure length of approximately 222 and 215 bp, respectively. No inverted terminal repeat (ITR) was detected. The ORF2 contained conserved replication initiator motif, NTP-binding and helicase domain similar to NS-1 of other parvoviruses. Therefore, it most likely encoded the major nonstructural protein (NS-1). The ORF1 encoded putative nonstructural protein-2 (NS-2) with unknown function. The ORF3 of the HPV genome encoded a capsid protein (VP) of approximately 92 kDa. This may be later cleaved after arginine residue to produce a 57-kDa structural protein. A phylogenetic tree based on conserved amino acid sequences (119 aa) revealed that it is closely related to Brevidensoviruses, which are shrimp parvovirus (IHHNV) and mosquito densoviruses (AaeDNV and AalDNV). However, the overall genomic organization and genome size of HPV were different from these parvoviruses, for instance, the non-overlapping of NS1 and NS2, the larger VP gene, and the bigger genome size. This suggested that this HPV virus is a new type in Parvoviridae family. We therefore propose to rename this virus P. monodon densovirus (PmDNV).

Genetic, biochemical, and structural characterization of a new densovirus isolated from a chronically infected Aedes albopictus C6/36 cell line

We report the isolation, sequencing, biochemical, and structural characterization of a previously undescribed virus in a chronically infected Aedes albopictus C6/36 cell line. This virus is identified as a new densovirus under the Densovirinae subfamily of the Parvoviridae based on its biological and morphologic properties as well as sequence homologies, and is tentatively designated A. albopictus C6/36 cell densovirus (C6/36 DNV). Analysis of the 4094 nt of the C6/36 DNV genome revealed that the plus strand had three large open reading frames (ORFs): a left ORF, a right ORF, and a mid-ORF (within the left ORF), whose potential coding capacities are 91.0, 40.8, and 41.2 kDa, respectively. The left ORF likely encodes the nonstructural protein NS-1, which contains NTP-binding and helicase domains. The right ORF likely encodes structural proteins, VP1 and VP2. Our analyses revealed that C6/36 DNV has a similar genomic organization and shares very high homology in nucleotide sequence and amino acid sequences with Aedes aegypti densovirus (AaeDNV) and A. albopictus densovirus (AalDNV), members of the genus Brevidensovirus of the Densovirinae. Similar to other densoviruses, C6/36 DNV has a different genomic organization and no recognizable sequence homology with viruses in the Parvovirinae. The three-dimensional (3D) reconstruction of the C6/36 DNV at 15.6-A resolution by electron cryomicroscopy (cryoEM) revealed distinctive outer surface features not previously seen in other parvoviruses, indicating structural divergence of densoviruses, in addition to its genomic differences, while the inner surface of the C6/36 DNV capsid exhibits features that are conserved among 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.

Comparison of penaeid shrimp and insect parvoviruses suggests that viral transfers may occur between two distantly related arthropod groups

The DNA and putative amino acid sequences of representative insect and shrimp parvoviruses (subfamily Densovirinae) were analyzed using computer programs. Shrimp viruses included hepatopancreatic parvovirus (HPV) of Penaeus monodon (HPVmon) and P. chinensis (HPVchin), spawner-isolated mortality virus from P. monodon (SMVmon) and infectious hypodermal and hematopoietic necrosis virus (IHHNV) from P. vannamei. Insect viruses included Aedes aegypti densovirus (AaeDNV), Aedes albopictus densovirus (AalDNV), Junonia coenia densovirus (JcDNV), Galleria mellonella densovirus (GmDNV), Bombyx mori densovirus 5 (BmDNV), Diatraea saccharalis densovirus (DsDNV) and Periplaneta fuliginosa densovirus (PfDNV). Virion size for all these viruses ranged between 18 and 30 nm diameter and ssDNA genome length was between 4 and 6 kb. Using BLAST or Clustal W with the sequence fragments available, no significant DNA homology was found except for 77% DNA identity between HPVmon and HPVchin. However, phylogenetic trees constructed by comparing DNA genome sequences for putative viral polypeptides, capsid proteins and nonstructural proteins placed the parvoviruses into two Clades: Clade 1 with SMVmon, PfDNV, DsDNV, GmDNV, JcDNV, and BmDNV; and Clade 2 with HPVmon, HPVchin, IHHNV, AalDNV and AaeDNV. The four shrimp parvoviruses fell into two different clades that grouped with different insect parvoviruses.

Extrusion of an imperfect palindrome to a cruciform in superhelical DNA: complete determination of energetics using a statistical mechanical model

We present a detailed study of the extrusion of an imperfect palindrome, derived from the terminal regions of vaccinia virus DNA and contained in a superhelical plasmid, into a cruciform containing bulged bases. We monitor the course of extrusion by two-dimensional gel electrophoresis experiments as a function of temperature and linking number. We find that extrusion pauses at partially extruded states as negative superhelicity increases. To understand the course of extrusion with changes in linking number, DeltaLk, we present a rigorous semiempirical statistical mechanical analysis that includes complete coupling between DeltaLk, cruciform extrusion, formation of extrahelical bases, and temperature-dependent denaturation. The imperfections in the palindrome are sequentially incorporated into the cruciform arms as hairpin loops, single unpaired bases, and complex local regions containing several unpaired bases. We analyze the results to determine the free energies, enthalpies and entropies of formation of all local structures involved in extrusion. We find that, for each unpaired structure, the DeltaG, DeltaH and DeltaS of formation are all approximately proportional to the number of unpaired bases contained therein. This surprising result holds regardless of the arrangement or composition of unpaired bases within a particular structure. Imperfections have major effects on the overall energetics of cruciform extrusion and on the course of this transition. In particular, the extent of the DeltaLk change necessary to extrude an imperfect palindrome is considerably greater than that required for extrusion of the underlying perfect palindrome. Our analysis also suggests that, at higher temperatures, significant denaturation at the base of an imperfect cruciform can successfully compete with extension of the cruciform arms.

Genome organization of Casphalia extranea densovirus, a new iteravirus

The viral genome of Casphalia extranea densovirus (CeDNV) has been cloned and sequenced. It was 5002 nucleotides long and contained inverted terminal repeats of 230 nucleotides. Their distal 159 nucleotides formed imperfect palindromes in two orientations. Three large open reading frames (ORFs) were identified on the same strand, two in the left-hand half and one in the right-hand half. Each of the five structural proteins, expressed from the right-hand ORF in the baculovirus system, autoassembled into capsids. The two left-hand ORFs overlapped and code for nonstructural (NS) proteins. NS1 protein was shown to contain replicator protein and helicase/ATPase motifs. The PGY region in VP1 capsid protein is conserved among most parvoviruses and contained a phospholipase A(2) motif, a novel viral enzyme. This domain was expressed and its enzyme activity was demonstrated. The approximate 75% sequence identity between the DNAs from CeDNV and BmDNV-1 and identical genome organization indicated that CeDNV should be classified in the Iteravirus genus.

Biochemical characterization of Junonia coenia densovirus nonstructural protein NS-1

Junonia coenia densovirus (JcDNV) is an autonomous parvovirus that infects the larvae of the common buckeye butterfly, Junonia coenia. Unlike vertebrate parvoviruses, the genes encoding the structural protein and nonstructural (NS) proteins of JcDNV are in opposite orientations; thus, each strand contains a sense and antisense open reading frame (ORF). The promoter at map position 93 controls expression of NS ORFs 2, 3, and 4, which encode three NS proteins, NS-1, NS-2, and NS-3. These proteins are likely to be involved in viral DNA replication, among other functions. In contrast to the nonstructural proteins of the vertebrate parvoviruses, the NS proteins of the Densovirinae have not been characterized. Here, we describe biochemical properties of the NS-1 protein of JcDNV. The NS-1 ORF was cloned in frame with the Escherichia coli malE gene, which encodes the bacterial maltose binding protein (MBP). Using electrophoretic mobility shift and DNase I protection assays, we identified the region of the JcDNV terminal sequence that is recognized specifically by the MBP-NS-1 fusion protein. The site consists of (GAC)4 and is located on the A-A' region of the terminal palindrome. In addition, the MBP-NS-1 fusion protein catalyzes the cleavage of single-stranded DNA (ssDNA) substrates derived from the JcDNV putative origin of replication, primarily at two sites in the motif 5'-G*TAT*TG-3'. One cleavage site is between the thymidine dinucleotide at positions 92 and 93 and the other site corresponds to thymidine at nucleotide 95; both sites are on the complementary strand of the sequence assigned GenBank accession number A12984. Cleavage of ssDNA is dependent on the presence of a divalent metal cofactor but does not require nucleoside triphosphate hydrolysis. Parvovirus NS proteins contain the phylogenically conserved Walker A- and B-site ATPase motifs. These sites in JcDNV NS-1 diverge from the consensus, yet despite these atypical motifs our analyses support that MBP-NS-1 has ATP-dependent helicase activity. These results indicate that JcDNV NS-1 possesses activities common to the superfamily of rolling-circle replication initiator proteins in general and the parvovirus replication proteins in particular, and they provide a basis for comparative analyses of the structure and function relationships among the parvovirus NS-1 equivalents.

Genome organization of the densovirus from Bombyx mori (BmDNV-1) and enzyme activity of its capsid

Bombyx mori densovirus (BmDNV-1), on the basis of the previously reported genome sequence, constitutes by itself a separate genus (Iteravirus) within the Densovirinae subfamily of parvoviruses. Inconsistencies in the genome organization, however, necessitated its reassessment. The genome sequence of new clones was determined and resulted in a completely different genome organization. The corrected sequence also contained conserved sequence motifs found in other parvoviruses. Some amino acids in the highly conserved domain in the unique region of VP1 were shared by critical amino acids in the catalytic site and Ca(2+)-binding loop of secreted phospholipase A2, such as from snake and bee venoms. Expression of this domain and determination of enzyme activity demonstrated that capsids have a phospholipase A2 activity thus far unknown to occur in viruses. This viral phospholipase A2, which is required shortly after entry into the cell, showed a substrate preference for phosphatidylethanolamine and phosphatidylcholine over phosphatidylinositol.

Infectious hypodermal and hematopoietic necrosis virus of shrimp is related to mosquito brevidensoviruses

We purified and sequenced infectious hypodermal and hematopoietic necrosis virus (IHHNV), a small DNA virus of shrimp, from wild Penaeus stylirostris. The virion has a buoyant density of 1.45 as determined by cesium chloride gradient. Analysis of 3873 nucleotides of the viral genome revealed three large open reading frames (ORFs) and parts of the noncoding termini of the viral genome. The left, mid, and right ORFs on the complementary (plus) strand have potential coding capacities of 666 amino acids (aa) (75.77 kDa), 363 aa (42.11 kDa), and 329 aa (37.48 kDa), respectively. The overall genomic organization is similar to that of the mosquito brevidensoviruses. The left ORF most likely encodes the major nonstructural (NS) protein (NS-1) since it contains conserved replication initiator motifs and NTP-binding and helicase domains similar to those in NS-1 from all other parvoviruses. The IHHNV putative NS-1 shares the highest aa sequence homology with the NS-1 of mosquito brevidensoviruses, Aedes densovirus and Aedes albopictus parvovirus. A search for putative splicing sites revealed that the N-terminal region of NS-1 is very likely located in a small ORF upstream of the left ORF. The right ORF is presumed to encode structural polypeptides (VPs), as in other parvoviruses. Two putative promoters, located upstream of the left and right ORFs, are presumed to regulate expression of NS and VP genes, respectively. Thus, IHHNV is closely related to densoviruses of the genus Brevidensovirus in the family Parvoviridae, and we therefore propose to rename this virus Penaeus stylirostris densovirus (PstDNV).

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

The nucleotide sequence of GmDNV, an insect parvovirus, reveals large open reading frames (ORFs) on both strands of the viral replicative form DNA. Previously, we identified two viral transcripts within the polyadenylated RNA fraction of infected host larvae (Gross et al., 1990, J. Invertebr. Pathol. 56, 175-180). In this work we used hybridization of single-stranded, unidirectional probes to RNA blots to show that the two transcripts, synthesized in vivo in GmDNV-infected Galleria mellonella larvae, are of antiparallel orientation. To determine their coding specificities, polyadenylated RNAs were isolated from hybrids with DNA from the left and right halves of the viral genome and translated in a rabbit reticulocyte system. The "right," 2.4-kb hybrid-selected RNA was shown to direct the synthesis of four polypeptides that comigrated with the four viral capsid proteins and were immunoprecipitated with anti-GmDNV serum. Translation of the "left," 1.8-kb RNA yielded three polypeptides, none of which was detected among the viral capsid proteins. This type of expression strategy is unique among vertebrate and most invertebrate parvoviruses, which use only one DNA strand to encode all their proteins. On the other hand, the basic organization of parvoviruses, in which the regulatory and structural proteins are encoded, respectively, by two clusters of ORFs located at the left and right halves of the genome, is conserved.

Analysis of proteins encoded in the bipartite genome of a new type of parvo-like virus isolated from silkworm - structural protein with DNA polymerase motif

Bombyx mori densonucleosis virus type 2 (BmDNV-2) is a small, spherical virus containing two complementary single-stranded linear DNA molecules (VD1, VD2). BmDNV-2 is a new type of virus with a unique, yet unspecified replication mechanism which is different from that of parvoviruses (Bando, H., Choi, H., Ito, Y., Nakagaki, M. , Kawase, S., 1992. Structural analysis on the single-stranded genomic DNAs of the virus newly isolated from silkworm: the DNA molecules share a common terminal sequence, Arch. Virol. 124, 187-193; Bando, H., Hayakawa, T., Asano, S., Sahara, K., Nakagaki, M. , Iizuka, T., 1995. Analysis of the genetic information of a DNA segment of a new virus from silkworm, Arch. Virol., 140, 1147-1155; Hayakawa, T., Asano, S., Sahara, K., Iizuka, T., Bando, H., 1997. Detection of replicative intermediate with closed terminus of Bombyx densonucleosis virus. Arch. Virol. 142, 1-7). Recent analyses on the genomic information of BmDNV-2 identified open reading frames which code for three tentative nonstructural proteins and four (VP1 to 4) of the six known structural proteins (Bando, H., Hayakawa, T., Asano, S., Sahara, K., Nakagaki, M., Iizuka, T., 1995. Analysis of the genetic information of a DNA segment of a new virus from silkworm, Arch. Virol., 140, 1147-1155; Nakagaki et al., in preparation). In this report we demonstrate that the two largest ORFs, VD1-ORF1 and VD2-ORF1, code for the two remaining structural proteins. In addition, computer-assisted analysis revealed that the structural protein encoded in VD1-ORF1 contains sequences conserved among various DNA polymerases, and showed an evolutionary relationship with the DNA polymerases involved in protein-primed replication.

Analysis of the genetic information of a DNA segment of a new virus from silkworm

In 1983, a parvo-like virus (Yamanashi isolate) was newly isolated from silkworm. However, unlike parvovirus, two DNA molecules (VD1 and 2) were always extracted from purified virions. To investigate the structure and organization of the virus genomes, we determined the complete nucleotide sequence of VD2. The sequence consisted of 6031 nucleotides (nts) and contained a large open reading frame (ORF1) with 3513 nts. A smaller open reading frame (ORF2) with 702 nts was found in the complementary sequence. Computer analysis revealed that both ORFs did not code for the major structural proteins (VP1, 2, 3, and 4). These results suggest that VD2 has not enough information to produce progeny virions by itself. Further, the structural importance of the terminal sequence (CTS) common to both VD1 and VD2 was also predicted by a computer analysis.

Structure, restriction map and infectivity of the genomic and replicative forms of AaPV DNA

We have characterized the genomic and replicative form (RF) DNA of the Aedes albopictus Parvovirus (AaPV), a virus isolated from a chronically infected C6/36 clone of Aedes albopictus cell line [22]. The genome of AaPV virions is a single-stranded linear DNA molecule approximately 4.2 kb in length, essentially (about 90%) encapsidated as minus strand. A restriction map of the RF DNA isolated from infected C6/36 cells was established. Among the 23 restriction enzymes tested, 14 cleaved the AaPV RF DNA and 30 restriction sites were mapped and oriented with respect to the viral genomic DNA. Both viral and RF DNAs were found infectious when transfected to virus-free C6/36 cells. The asymmetrical encapsidation of the viral genome is a property common to most vertebrate autonomous parvoviruses but rather unusual among densoviruses. Both by its small size, the asymmetrical mode of encapsidation and the restriction map, the AaPV genome resembles that of the Aedes Densonucleosis virus [1].

A densovirus newly isolated from the smoky-brown cockroach Periplaneta fuliginosa

We purified a causing agent of fetal disease for smoky-brown cockroach Periplaneta fuliginosa, which was designated as "cockroach small spherical virus (CSSV)". Purified virus particles had a diameter of 22 +/- 0.6 nm and contained DNA as a single-stranded form. However, the extraction of DNA under condition of appropriate high salt and elevated temperature yielded a double-stranded DNA with a size of 5,500 nucleotides. These results were quite similar to those of other densoviruses (DNVs). The CSSV had five structural proteins (VP1: 52 KDa, VP2: 56 KDa, VP3: 79 KDa, VP4: 82 KDa, and VP5: 105 KDa). The SDS-PAGE profile of these proteins was quite different from that of the cockroach DNV previously reported and was rather similar to that of Bombyx mori (Bm) DNV-1. An immunochemical study, however, demonstrated that there was no immunological relationship between the CSSV and the Bm DNV-1. These data suggest that the CSSV is a new member of DNV.

Complete nucleotide sequence of the cloned infectious genome of Junonia coenia densovirus reveals an organization unique among parvoviruses

We previously constructed a recombinant plasmid, pBRJ, encompassing an infectious Junonia coenia densovirus (JcDNV) genome (M. Jourdan et al. (1990). Virology 179, 403-409). We report here the complete viral sequence of pBRJ. The genome, 5908 nucleotides (nt) long, consists of an internal unique sequence flanked by long (517 nt) inverted terminal repeats. The first 96 bases of one extremity can fold into a typical Y-shaped hairpin structure. The opposite extremity is incomplete, lacking 88 nt. These terminal structures, similar to those of dependoviruses, human parvovirus B19 and Bombyx mori densovirus (BmDNV), strongly suggest a common mechanism of DNA replication for these parvoviruses. JcDNV genomic organization is unique among parvoviruses in that coding sequences are evenly distributed in the 5' half of both strands. On one strand, the major open reading frame (ORF1) encodes the four structural proteins. On the complementary strand, ORF2, ORF3 (included in ORF2), and ORF4 probably encode nonstructural proteins. JcDNV genome has little DNA homology with vertebrate parvoviruses and surprisingly even less with the two densoviruses presently sequenced. ORF1 contains the highly conserved PGY and G-rich regions and ORF2 the NTP-binding domain common to most structural and to all nonstructural vertebrate parvoviral ORFs, respectively. The single homology between JcDNV and BmDNV is unexpectedly located in JcDNV NTP-binding domain and BmDNV ORF2 assumed to encode structural polypeptides. Only a weak homology exists between JcDNV and Aedes DNV in their NTP-binding domain.

Structural analysis on the single-stranded genomic DNAs of the virus newly isolated from silkworm: the DNA molecules share a common terminal sequence

Recently, a parvo-like virus was newly isolated from silkworm larvae and the two viral DNAs (VD1 and VD2) with different electro-mobilities were identified. We cloned the viral DNAs in a plasmid pUC119 and demonstrated that these two DNAs were not a bimorphic molecules though they shared a common terminal sequence of 53 nucleotides. In addition, the sequence at the 5' terminus of each strand of the viral DNA was located in inverted form at its 3' terminus. On the other hand, the nucleotide sequences of VD1 and VD2 were different from that of the Bombyx densovirus (Ina isolate) DNA.

The densovirus of Junonia coenia (Jc DNV) as an insect cell expression vector

An infectious genome of the Junonia coenia densovirus (Jc DNV) has been recently cloned and sequenced. We investigated the ability of this cloned genome to be used as expression vector by inserting the lacZ gene of Escherichia coli as fusion gene in the major open reading frame (ORF 1) of the viral sequence. The resulting recombinant plasmid designated pBRJlac Z was transfected into insect SPC-SL 52 cells and the expression of beta-galactosidase (beta-gal) was detected qualitatively or quantitatively by using Xgal or ONPG as chromogenic substrates. Western blot analysis revealed that beta-gal was expressed as chimeric capsid-beta-gal polypeptides. This provided evidence that ORF1 codes for structural polypeptides which share a common C-terminal sequence. Construction of plasmids with alterations or deletions in ORF2, 3 or 4, allowed us to implicate nonstructural (NS) functions in viral DNA replication. Deletions in inverted terminal repeats or in NS functions did not abolish expression of capsid polypeptides but reduced it dramatically. Encapsidation of Jlac Z recombinant genome was achieved by trans-complementation with plasmids bearing intact structural and nonstructural functions. Detection of a beta-gal activity in SPC-SL 52 cells following several subcultures post-transfection suggests that Jlac Z recombinant genome could be maintained in an integrative or episomal state.

Nucleotide sequence and genomic organization of Aedes densonucleosis virus

Over 99% of the genome of Aedes densonucleosis virus was determined. Two types of the viral DNA were found that differ only in four nucleotides (nt) in the 5' noncoding part and whose sizes are 4009 nt (more copious) and 4012 nt, respectively. Both 146 nt at the 3' end and 164 nt at the 5' end could assume a similar T-shaped structure; but unlike the adeno-associated virus, Aedes DNA has a unique primary DNA sequence at each terminus. However, the crossarms of these structures are built of the same sequences. An imperfect direct repeat of 34 nt was observed in the 5' noncoding part. The plus strand has three large open reading frames (ORF): a left ORF, a right ORF, and a mid ORF (within the left ORF). The left ORF codes for the nonstructural protein NS-1 (97.5K) featured by an NTP-binding domain, and the right ORF encodes the both capsid proteins, the smaller of which (39K) is supposed to be derived from the larger one (40.5K) by proteolytic cleavage. There is also an ORF in the minus strand. The putative polypeptide coded by this ORF is extremely hydrophobic.

Restriction map of the Casphalia extranea densovirus genome

A physical map of the Casphalia extranea densovirus genome (CeDNV) was constructed. The size of the intact viral genome was estimated to be 4.9 kilobases or 1.6 MDa (single strand). The double-stranded CeDNV genomic DNA was cleaved with 26 restriction endonucleases and 20 restriction sites were mapped on the genome. The CeDNV DNA restriction map was compared to those of other densoviruses. Southern blotting hybridization experiments failed to reveal any homology between the genomes of CeDNV and Junoniacoenia densovirus (JcDNV).

Antineoplastic activity of parvoviruses

The family of Parvoviridae is composed of small, nuclear-replicating viruses that are without envelope and contain an essentially single-stranded, linear DNA genome. Certain parvoviruses proved to have the remarkable capacity to prevent the formation of spontaneous as well as virtually- and chemically-induced tumors in laboratory animals. Established tumor cells serve as targets for the antineoplastic activity of parvoviruses, since the growth of preformed cancer cells transplanted in recipient animals can also be inhibited by these viruses. Furthermore, epidemiological studies in humans have revealed a correlation between serological evidence of parvoviral infection and a lower incidence of certain cancers. The parvoviral life-cycle appears to depend on cellular factors that are expressed as a function of proliferation and differentiation. This subordination may account for the oncotropism of parvoviruses in vivo and for the specificity of their interactions with (pre-)neoplastic cells under appropriate culture conditions. Thus, certain parvoviruses were found to preferentially lyse initiated or stably transformed cells in vitro, as a possible result of the stimulation of the production and/or activity of cytotoxic viral proteins. Parvoviruses can also have a cytostatic effect and cause the reversion of transformation traits, parallel to the down-modulation of the expression of defined genes, in particular oncogenes. Such direct disturbance of neoplastic cells or their precursors may participate in the oncosuppressive activity of parvoviruses, although indirect viral effects mediated by host defense mechanisms also deserve to be considered. Altogether, these properties suggest the possible use of parvoviruses as probes to investigate the process of malignant transformation.(ABSTRACT TRUNCATED AT 250 WORDS)