Preliminary x-ray characterization of authentic providence virus and attempts to express its coat protein gene in recombinant baculovirus

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.

Nucleic acid packaging in viruses

We review recent literature describing protein nucleic acid interactions and nucleic acid organization in viruses. The nature of the viral genome determines its overall organization and its interactions with the capsid protein. Genomes composed of single strand (ss) RNA and DNA are highly flexible and, in some cases, adapt to the symmetry of the particle-forming protein to show repeated, sequence independent, nucleoprotein interactions. Genomes composed of double-stranded (ds) DNA do not interact strongly with the container due to their intrinsic stiffness, but form well-organized layers in virions. Assembly of virions with ssDNA and ssRNA genomes usually occurs through a cooperative condensation of the protein and genome, while dsDNA viruses usually pump the genome into a preformed capsid with a strong, virally encoded, molecular motor complex. We present data that suggest the packing density of ss genomes and ds genomes are comparable, but the latter exhibit far higher pressures due to their stiffness.

Evolution in action: N and C termini of subunits in related T = 4 viruses exchange roles as molecular switches

The T = 4 tetravirus and T = 3 nodavirus capsid proteins undergo closely similar autoproteolysis to produce the N-terminal beta and C-terminal, lipophilic gamma polypeptides. The gamma peptides and the N termini of beta also act as molecular switches that determine their quasi equivalent capsid structures. The crystal structure of Providence virus (PrV), only the second of a tetravirus (the first was NomegaV), reveals conserved folds and cleavage sites, but the protein termini have completely different structures and the opposite functions of those in NomegaV. N termini of beta form the molecular switch in PrV, whereas gamma peptides play this role in NomegaV. PrV gamma peptides instead interact with packaged RNA at the particle two-folds by using a repeating sequence pattern found in only four other RNA- or membrane-binding proteins. The disposition of peptide termini in PrV is closely related to those in nodaviruses, suggesting that PrV may be closer to the primordial T = 4 particle than NomegaV.

Evidence of prior exposure to human bocavirus as determined by a retrospective serological study of 404 serum samples from adults in the United States

Recently, molecular screening for pathogenic agents has identified a partial genome of a novel parvovirus, called human bocavirus (HBoV). The presence of this newly described parvovirus correlated with upper and lower respiratory tract infections in children. Lower respiratory tract infections are a leading cause of hospital admission in children, and the etiological agent has not been identified in up to 39% of these cases. Using baculovirus expression vectors (BEVs) and an insect cell system, we produced virus-like particles (VLPs) of HBoV. The engineered BEVs express the HBoV capsid proteins stoichiometrically from a single open reading frame. Three capsid proteins assemble into the VLP rather than two proteins predicted from the HBoV genome sequence. The denatured capsid proteins VP1, VP2, and VP3 resolve on silver-stained sodium dodecyl sulfate-polyacrylamide gels as three bands with apparent molecular masses of 72 kDa, 68 kDa, and 62 kDa, respectively. VP2 apparently initiates at a GCT codon (alanine) 273 nucleotides downstream from the VP1 start site and 114 nucleotides upstream from the VP3 initiation site. We characterized the stable capsids using physical, biochemical, and serological techniques. We found that the density of the VLP is 1.32 g/cm(3) and is consistent with an icosahedral symmetry with approximately a 25-nm diameter. Rabbit antiserum against the capsid of HBoV, which did not cross-react with adeno-associated virus type 2, was used to develop enzyme-linked immunosorbent assays (ELISAs) for anti-HBoV antibodies in human serum. Using ELISA, we tested 404 human serum samples and established a range of antibody titers in a large U.S. adult population sample.

Induction of apoptosis in Saccharomyces cerevisiae results in the spontaneous maturation of tetravirus procapsids in vivo

The Tetraviridae are a family of small, non-enveloped, insect RNA viruses consisting of one or two single-stranded, positive-sense genomic RNAs encapsidated in an icosahedral capsid with T=4 symmetry. Tetravirus procapsids undergo maturation when exposed to a low pH environment in vitro. While the structural biology of the conformational changes that mediate acid-dependent maturation is well understood, little is known about the significance of acid-dependent maturation in vivo. To address this question, the capsid-coding sequence of the tetravirus Helicoverpa armigera stunt virus was expressed in Saccharomyces cerevisiae cells. Virus-like particles were shown to assemble as procapsids that matured spontaneously in vivo as the cells began to age. Growth in the presence of hydrogen peroxide or acetic acid, which induced apoptosis or programmed cell death in the yeast cells, resulted in virus-like particle maturation. The results demonstrate that assembly-dependent maturation of tetravirus procapsids in vivo is linked to the onset of apoptosis in yeast cells. We propose that the reduction in pH required for tetraviral maturation may be the result of cytosolic acidification, which is associated with the early onset of programmed cell death in infected cells.