Rearranged genomic RNA segments offer a new approach to the reverse genetics of rotaviruses

Group A rotaviruses (RV), members of the Reoviridae family, are a major cause of infantile acute gastroenteritis. The RV genome consists of 11 double-stranded RNA segments. In some cases, an RNA segment is replaced by a rearranged RNA segment, which is derived from its standard counterpart by partial sequence duplication. We report here a reverse genetics system for RV based on the preferential packaging of rearranged RNA segments. Using this system, wild-type or in vitro-engineered forms of rearranged segment 7 from a human rotavirus (encoding the NSP3 protein), derived from cloned cDNAs and transcribed in the cytoplasm of COS-7 cells with the help of T7 RNA polymerase, replaced the wild-type segment 7 of a bovine helper virus (strain RF). Recombinant RF viruses (i.e., engineered monoreassortant RF viruses) containing an exogenous rearranged RNA were recovered by propagating the viral progeny in MA-104 cells, with no need for additional selective pressure. Our findings offer the possibility to extend RV reverse genetics to segments encoding nonstructural or structural proteins for which no potent selective tools, such as neutralizing antibodies, are available. In addition, the system described here is the first to enable the introduction of a mutated gene expressing a modified nonstructural protein into an infectious RV. This reverse genetics system offers new perspectives for investigating RV protein functions and developing recombinant live RV vaccines containing specific changes targeted for attenuation.

Human antibody responses to bovine (Newbury-2) norovirus (GIII.2) and association to histo-blood group antigens

Serum antibodies to bovine norovirus have been found recently in about 22% of humans. Whether this prevalence reflects limited virulence properties of the virus or that inherited host factors provide protection against bovine norovirus infection in humans remains to be established. To investigate whether histo-blood group antigens correlate with the presence of bovine norovirus (GIII.2) antibody, plasma (n = 105) from Swedish blood donors, genotyped and phenotyped for secretor, Lewis and ABO, were tested and compared for the frequency of IgG antibody and antibody titer to Bo/Newbury2/76/UK. In total, 26.7% (28/105) of Swedish blood donors were antibody-positive. Two non-secretors (2/21, 9.5%) were antibody-positive compared with 26/84 (31%) secretors (P = 0.047). While no statistically significant correlation was found between the frequency of antibodies to bovine norovirus and different ABO blood groups, individuals with blood type B presented the highest frequency of antibodies (37.5%) compared with 0-30% among other blood groups. Individuals with Le(a-b+) had not only higher frequency of antibodies (31.3%) compared with Le(a+b-) (11%) (P = 0.068) but also higher antibody titer (P = 0.085) although this was not significant statistically. No detectable cross-reaction between bovine GIII.2 and human GII.3 NoV VLP was found with human and animal sera. The results of this study suggest that bovine norovirus infections occur in Sweden and that secretor status but not ABO blood groups is a possible risk factor for infection.

The rotaviral NSP3 protein stimulates translation of polyadenylated target mRNAs independently of its RNA-binding domain

The non-structural protein 3 (NSP3) of rotaviruses is an RNA-binding protein that specifically recognises a 4 nucleotide sequence at the 3' extremity of the non-polyadenylated viral mRNAs. NSP3 also has a high affinity for eIF4G. These two functions are clearly delimited in separate domains the structures of which have been determined. They are joined by a central domain implicated in the dimerisation of the full length protein. The bridging function of NSP3 between the 3' end of the viral mRNA and eIF4G has been proposed to enhance the synthesis of viral proteins. However, this role has been questioned as knock-down of NSP3 did not impair viral protein synthesis. We show here using a MS2/MS2-CP tethering assay that a C-terminal fragment of NSP3 containing the eIF4G binding domain and the dimerisation domain can increase the expression of a protein encoded by a target reporter mRNA in HEK 293 cells. The amount of reporter mRNA in the cells is not significantly affected by the presence of the NSP3 derived fusion protein showing that the enhanced protein expression is due to increased translation. These results show that NSP3 can act as a translational enhancer even on a polyadenylated mRNA that should be a substrate for PABP1.

The alphaGal epitope of the histo-blood group antigen family is a ligand for bovine norovirus Newbury2 expected to prevent cross-species transmission

Among Caliciviridae, the norovirus genus encompasses enteric viruses that infect humans as well as several animal species, causing gastroenteritis. Porcine strains are classified together with human strains within genogroup II, whilst bovine norovirus strains represent genogroup III. Various GI and GII human strains bind to carbohydrates of the histo-blood group family which may be shared among mammalian species. Genetic relatedness of human and animal strains as well as the presence of potentially shared ligands raises the possibility of norovirus cross-species transmission. In the present study, we identified a carbohydrate ligand for the prototype bovine norovirus strain Bo/Newbury2/76/UK (NB2). Attachment of virus-like particles (VLPs) of the NB2 strain to bovine gut tissue sections showed a complete match with the staining by reagents recognizing the Galalpha1,3 motif. Alpha-galactosidase treatment confirmed involvement of a terminal alpha-linked galactose. Specific binding of VLPs to the alphaGal epitope (Galalpha3Galbeta4GlcNAcbeta-R) was observed. The binding of Galalpha3GalalphaOMe to rNB2 VLPs was characterized at atomic resolution employing saturation transfer difference (STD) NMR experiments. Transfection of human cells with an alpha1,3galactosyltransferase cDNA allowed binding of NB2 VLPs, whilst inversely, attachment to porcine vascular endothelial cells was lost when the cells originated from an alpha1,3galactosyltransferase KO animal. The alphaGal epitope is expressed in all mammalian species with the exception of the Hominidaea family due to the inactivation of the alpha1,3galactosyltransferase gene (GGTA1). Accordingly, the NB2 carbohydrate ligand is absent from human tissues. Although expressed on porcine vascular endothelial cells, we observed that unlike in cows, it is not present on gut epithelial cells, suggesting that neither man nor pig could be infected by the NB2 bovine strain.

Comparison of the efficacy of rotavirus VLP vaccines to a live homologous rotavirus vaccine in a pig model of rotavirus disease

Rotavirus-like particles (VLPs) have shown promise as rotavirus vaccine candidates in mice, rabbits and pigs. In pigs, VLP vaccines reduced rotavirus shedding and disease but only when used in conjunction with live attenuated human rotavirus. Using a porcine rotavirus pig model, rotavirus antigen shedding was reduced by up to 40% after vaccination with VLPs including the neutralizing antigens VP7 and VP8* when used in combination with the adjuvant polyphosphazene poly[di(carbozylatophenoxy)phoshazene] (PCPP). In contrast, complete protection from rotavirus antigen shedding and disease was induced by vaccination with the virulent porcine rotavirus PRV 4F. This is the first study to demonstrate some post-challenge reductions in rotavirus antigen shedding in a pig model of rotavirus disease after vaccination with VLPs without combining with infectious rotavirus.

Parenteral administration of RF 8-2/6/7 rotavirus-like particles in a one-dose regimen induce protective immunity in mice

Rotavirus virus-like particles (RV-VLPs) represent a novel strategy for development of a rotavirus subunit vaccine. In this study, RF 8-2/6/7-VLPs with rotavirus VP8 protein (amino acid 1-241 of VP4) fused to the amino terminal end of a truncated VP2, were evaluated for their immunogenic and protective properties. A single intramuscular dose of, either 2 or 20 microg, RF 8-2/6/7-VLPs alone or combined with a potent adjuvant poly[di(carboxylatophenoxy)]phosphazene] (PCPP) induced rotavirus-specific serum IgG and IgA, fecal IgG titers that were enhanced 5-90-fold by adjuvant. Passive protective immunity was achieved in offspring to dams vaccinated with 2 and 20 microg RV-VLPs in presence of adjuvant and 20 microg RV-VLP without adjuvant.

Endoplasmic reticulum stress induces calcium-dependent permeability transition, mitochondrial outer membrane permeabilization and apoptosis

The accumulation of Ca2+ in the mitochondrial matrix can stimulate oxidative phosphorylation, but can also, at high Ca2+ concentrations, transmit and amplify an apoptotic signal. Here, we characterized the capacity of physiological stimuli (for example, histamine and inositol-1,4,5-triphosphate) and inducers of endoplasmic reticulum (ER) stress (for example, A23187, thapsigargin and tunicamycin) to release Ca2+ from ER stores, induce mitochondrial Ca2+ accumulation, and trigger cell death in human cervix and colon carcinoma cell lines. Sustained Ca2+ accumulation in the mitochondrial matrix induced by ER stress triggered signs of proapoptotic mitochondrial alteration, namely permeability transition, dissipation of the electrochemical potential, matrix swelling, relocalization of Bax to mitochondria and the release of cytochrome c and apoptosis-inducing factor from mitochondria. In contrast, rapid and transient accumulation of Ca2+ induced by physiological stimuli failed to promote mitochondrial permeability transition and to affect cell viability. The specificity of this apoptosis pathway was validated in cells using a panel of pharmacological agents that chelate Ca2+ (BAPTA-AM) or inhibit inositol-1,4,5-trisphosphate receptor (IP(3)R; 2-aminoethoxydiphenyl borate), voltage-dependent anion channel (VDAC) (4,4'-diisothiocyanatostilbene-2,2'-disulfonate, NADH), the permeability transition pore (cyclosporin A and bongkrekic acid), caspases (z-VAD-fmk) and protein synthesis (cycloheximide). Finally, we designed an original cell-free system in which we confronted purified mitochondria and ER vesicles, and identified IP(3)R, VDAC and the permeability transition pore as key proteins in the ER-triggered proapoptotic mitochondrial membrane permeabilization process.

Distribution and phenotype of rotavirus-specific B cells induced during the antigen-driven primary response to 2/6 virus-like particles administered by the intrarectal and the intranasal routes

Selection of mucosal sites is an important step in mucosal vaccine development. The intrarectal (IR) route represents an alternative to the oral route of immunization; nevertheless, immune responses induced by this route are not well defined. Here, we studied the early primary B cell response (induction, homing, and phenotype) induced by IR immunization with rotavirus (RV)-2/6 virus-like particles (VLP). Using flow cytometry, we traced RV-specific B cells in different lymphoid tissues and analyzed the expression of alpha4beta7 and CCR9, which are important receptors for homing to the gut, as well as CD5, a marker expressed by B1-a cells, which are a major source of natural antibodies. We observed a massive, specific B cell response in rectal follicles, lumbar, and mesenteric lymph nodes but not in Peyer's patches or cervical lymph nodes. A minority of cells expressed alpha4beta7, suggesting a probable lack of migration to the gut, whereas CCR9 and CD5 were expressed by 30-50% and 30-75% of specific B cells, respectively. Then, we compared the intranasal route of immunization and observed similar B cell frequency and phenotype but in respiratory lymphoid tissues. These results confirm the high compartmentalization of B cell responses within the mucosal system. They show that CCR9 expression, conversely to alpha4beta7, is not restricted to B cells induced in the gut. Finally, an important part of the RV-specific B cell response induced at the mucosal level during the primary response to VLP is most likely a result of B1-a cells.

Bone marrow dendritic cells internalize live RF-81 bovine rotavirus and rotavirus-like particles (RF 2/6-GFP-VLP and RF 8*2/6/7-VLP) but are only activated by live bovine rotavirus

Dendritic cells (DC) represent the link between innate and adaptive immunity. They are classified as antigen-presenting cells (APC) and can initiate and modulate the immune response. To investigate the interaction with DCs, live RF-81 bovine rotavirus strain (RFV) and rotavirus-like particles (rota-VLP), RF 2/6-GFP-VLP and rota RF 8*2/6/7-VLP, were added in vitro to murine bone marrow-derived DCs (bmDCs). Live RFV, RF 2/6-GFP-VLP and RF 8*2/6/7-VLP all bound to bmDC and were internalized but only live RFV stimulated phenotypic maturation of the bmDCs as shown by the upregulation of the co-stimulatory molecule CD86. Even though bmDCs internalized RF 2/6-GFP-VLP and RF 8*2/6/7-VLP as efficiently as live RFV, these rota-VLP were not able to activate the cells. Supernatants derived from bmDC cultures treated with live RFV, RF 2/6-GFP-VLP or RF 8*2/6/7-VLP were examined for TNF-alpha production. At 6, 18 and 24 h post-infection, TNF-alpha concentrations were significantly increased in cultures treated with live RFV and rota-VLP compared with untreated cultures. In conclusion, this study showed that live RF-81 bovine rotavirus strain was internalized and induced bmDCs activation, whereas both RF 2/6-GFP-VLP and RF 8*2/6/7-VLP were internalized by bmDCs without triggering their activation.

Structure-function analysis of the interaction between Bax and the cytomegalovirus-encoded protein vMIA

The viral mitochondrial inhibitor of apoptosis (vMIA) encoded by the human cytomegalovirus exerts cytopathic effects and neutralizes the proapoptotic endogenous Bcl-2 family member Bax by recruiting it to mitochondria, inducing its oligomerization and membrane insertion. Using a combination of computational modeling and mutational analyses, we addressed the structure-function relationship of the molecular interaction between the protein Bax and the viral antiapoptotic protein vMIA. We propose a model in which vMIA exhibits an overall fold similar to Bcl-X(L). In contrast to Bcl-X(L), however, this predicted conformation of vMIA does not bind to the BH3 domain of Bax and rather engages in electrostatic interactions that involve a stretch of amino acids between the BH3 and BH2 domains of Bax and an alpha-helical domain located within the previously defined Bax-binding domain of vMIA, between the putative BH1-like and BH2-like domains. According to this model, vMIA is likely to bind Bax preferentially in its membrane-inserted conformation. The capacity of vMIA to cause fragmentation of the mitochondrial network and disorganization of the actin cytoskeleton is independent of its Bax-binding function. We found that Delta131-147 vMIA mutant, which lacks both the Bax-binding function and cell-death suppression but has intact mitochondria-targeting capacity, is similar to vMIA in its ability to disrupt the mitochondrial network and to disorganize the actin cytoskeleton. vMIADelta131-147 is a dominant-negative inhibitor of the antiapoptotic function of wild-type vMIA. Our experiments with vMIADelta131-147 suggest that vMIA forms homo-oligomers, which may engage in cooperative and/or multivalent interactions with Bax, leading to its functional neutralization.

Modeling rotavirus-like particles production in a baculovirus expression vector system: Infection kinetics, baculovirus DNA replication, mRNA synthesis and protein production

Rotavirus is the most common cause of severe diarrhoea in children worldwide, responsible for more than half a million deaths in children per year. Rotavirus-like particles (Rota VLPs) are excellent vaccine candidates against rotavirus infection, since they are non-infectious, highly immunogenic, amenable to large-scale production and safer to produce than those based on attenuated viruses. This work focuses on the analysis and modeling of the major events taking place inside Spodoptera frugiperda (Sf-9) cells infected by recombinant baculovirus that may be critical for the expression of rotavirus viral proteins (VPs). For model validation, experiments were performed adopting either a co-infection strategy, using three monocistronic recombinant baculovirus each one coding for viral proteins VP(2), VP(6) and VP(7), or single-infection strategies using a multigene baculovirus coding for the three proteins of interest. A characteristic viral DNA (vDNA) replication rate of 0.19+/-0.01 h(-1) was obtained irrespective of the monocistronic or multigene vector employed, and synthesis of progeny virus was found to be negligible in comparison to intracellular vDNA concentrations. The timeframe for vDNA, mRNA and VP synthesis tends to decrease with increasing multiplicity of infection (MOI) due to the metabolic burden effect. The protein synthesis rates could be ranked according to the gene size in the multigene experiments but not in the co-infection experiments. The model exhibits acceptable prediction power of the dynamics of intracellular vDNA replication, mRNA synthesis and VP production for the three proteins involved. This model is intended to be the basis for future Rota VLPs process optimisation and also a means to evaluating different baculovirus constructs for Rota VLPs production.

Rectal immunization with rotavirus virus-like particles induces systemic and mucosal humoral immune responses and protects mice against rotavirus infection

To evaluate whether the rectal route of immunization may be used to provide appropriate protection against enteric pathogens such as rotaviruses (RV), we studied the antibody response and the protection induced by rectal immunization of mice with RV virus-like particles (VLP). For this purpose, 6-week-old BALBc mice were rectally immunized twice with RV 8-2/6/7-VLP derived from the bovine RV RF81 strain either alone or combined with various adjuvants including four toxins [cholera toxin (CT) and three attenuated Escherichia coli-derived heat-labile toxins (LTs), LT(R192G), LT(R72), and LT(K63)] and two Toll-like receptor-targeting adjuvants (CpG and resiquimod). Six weeks after the second immunization, mice were challenged with murine RV strain ECw. RV VLP administered alone were not immunogenic and did not protect mice against RV challenge. By contrast, RV VLP combined with any of the toxin adjuvants were immunogenic (mice developed significant titers of anti-RV immunoglobulin A [IgA] in both serum and feces and of anti-RV IgG in serum) and either efficiently induced complete protection of the mice (no detectable fecal virus shedding) or, for LT(K63), reduced the amount of fecal virus shedding after RV challenge. When combined with RV VLP, CpG and resiquimod failed to achieve protection, although CpG efficiently induced an antibody response to RV. These results support the consideration of the rectal route for the development of new immunization strategies against RV infection. Rectal delivery of a VLP-based vaccine might allow the use of adjuvants less toxic than, but as efficient as, CT.

Trypsin is associated with the rotavirus capsid and is activated by solubilization of outer capsid proteins

The rotavirus capsid is made up of three concentric protein layers. The outer layer, consisting of VP7 and VP4, is lost during virus entry into the host cell. Rotavirus field isolates can be adapted to high-titre growth in tissue culture by treatment with trypsin and by supplementing the culture medium with trypsin, which cleaves VP4 into two fragments, VP8* and VP5*. It is known that protease inhibitors reduce the replication of rotavirus in vitro and in vivo and also diminish disease symptoms in a mouse model. To clarify the molecular basis of these observations, a series of assays were conducted on purified rotavirus particles grown in the presence of trypsin. Results of HPLC and mass spectrometry followed by N-terminal sequencing showed that viral particles contain molecules of trypsin. When associated with triple-layer particles (TLPs), trypsin is inactive and not accessible to protease inhibitors, such as aprotinin. When the outer layer is solubilized by calcium-chelating agents, VP5*, VP8* and VP7 are released and the associated trypsin is activated, allowing cleavage of the viral capsid proteins, as well as other exogenous proteins. It is shown that addition of trypsin inhibitors significantly reduces synthesis of viral mRNA and viral proteins in cells and has a major inhibitory effect if present when virus enters the cell. These data indicate that incorporation of trypsin into rotavirus particles may enhance its infectivity.

Cytofluorometric quantitation of apoptosis-driven inner mitochondrial membrane permeabilization

The mitochondrial matrix can be specifically labeled by loading cells with calcein and simultaneous quenching of the non-mitochondrial calcein fluorescence with cobalt (Co2+). Positive staining of mitochondria thus requires that the inner mitochondrial membrane functions as a barrier separating calcein (within the matrix) from Co2+ (outside of the matrix). Upon induction of apoptosis, such calcein/Co2+ -labeled cells, demonstrate a decrease in the overall calcein fluorescence resulting from inner mitochondrial membrane permeabilization. This decrease can be quantified by cytofluorometry and can be dissociated from other apoptosis-associated mitochondrial perturbations such as the loss of the mitochondrial transmembrane potential (delta phi m), the local overproduction of re-active oxygen species, and the mitochondrial release of cytochrome c. In some paradigms of apoptosis the loss of calcein/Co2+ (CC) staining can be dissociated from the delta phi m loss, both of which may occur in a caspase-dependent or caspase-independent fashion, depending on the apoptosis inducer. Importantly, inner membrane permeabilization to CC may occur without a permanent delta phi m dissipation in apoptosis, suggesting that transient permeabilization events could participate at the apoptotic cascade. Altogether, our data demonstrate that inner mitochondrial membrane permeabilization constitutes an early event in the apoptotic cascade.

RoXaN, a novel cellular protein containing TPR, LD, and zinc finger motifs, forms a ternary complex with eukaryotic initiation factor 4G and rotavirus NSP3

Rotavirus mRNAs are capped but not polyadenylated, and viral proteins are translated by the cellular translation machinery. This is accomplished through the action of the viral nonstructural protein NSP3, which specifically binds the 3' consensus sequence of viral mRNAs and interacts with the eukaryotic translation initiation factor eIF4G I. To further our understanding of the role of NSP3 in rotavirus replication, we looked for other cellular proteins capable of interacting with this viral protein. Using the yeast two-hybrid assay, we identified a novel cellular protein-binding partner for rotavirus NSP3. This 110-kDa cellular protein, named RoXaN (rotavirus X protein associated with NSP3), contains a minimum of three regions predicted to be involved in protein-protein or nucleic acid-protein interactions. A tetratricopeptide repeat region, a protein-protein interaction domain most often found in multiprotein complexes, is present in the amino-terminal region. In the carboxy terminus, at least five zinc finger motifs are observed, further suggesting the capacity of RoXaN to bind other proteins or nucleic acids. Between these two regions exists a paxillin leucine-aspartate repeat (LD) motif which is involved in protein-protein interactions. RoXaN is capable of interacting with NSP3 in vivo and during rotavirus infection. Domains of interaction were mapped and correspond to the dimerization domain of NSP3 (amino acids 163 to 237) and the LD domain of RoXaN (amino acids 244 to 341). The interaction between NSP3 and RoXaN does not impair the interaction between NSP3 and eIF4G I, and a ternary complex made of NSP3, RoXaN, and eIF4G I can be detected in rotavirus-infected cells, implicating RoXaN in translation regulation.

Differential modulation of Bordetella pertussis virulence genes as evidenced by DNA microarray analysis

The production of most factors involved in Bordetella pertussis virulence is controlled by a two-component regulatory system termed BvgA/S. In the Bvg+ phase virulence-activated genes (vags) are expressed, and virulence-repressed genes (vrgs) are down-regulated. The expression of these genes can also be modulated by MgSO(4) or nicotinic acid. In this study we used microarrays to analyse the influence of BvgA/S or modulation on the expression of nearly 200 selected genes. With the exception of one vrg, all previously known vags and vrgs were correctly assigned as such, and the microarray analyses identified several new vags and vrgs, including genes coding for putative autotransporters, two-component systems, extracellular sigma factors, the adenylate cyclase accessory genes cyaBDE, and two genes coding for components of a type III secretion system. For most of the new vrgs and vags the results of the microarray analyses were confirmed by RT-PCR analysis and/or lacZfusions. The degree of regulation and modulation varied between genes, and showed a continuum from strongly BvgA/S-activated genes to strongly BvgA/S-repressed genes. The microarray analyses also led to the identification of a subset of vags and vrgs that are differentially regulated and modulated by MgSO(4) or nicotinic acid, indicating that these genes may be targets for multiple regulatory circuits. For example, the expression of bilA, a gene predicted to encode an intimin-like protein, was found to be activated by BvgA/S and up-modulated by nicotinic acid. Furthermore, surprisingly, in the strain analysed here, which produces only type 2 fimbriae, the fim3 gene was identified as a vrg, while fim2 was confirmed to be a vag.

Rotavirus nonstructural protein NSP5 interacts with major core protein VP2

Rotavirus is a nonenveloped virus with a three-layered capsid. The inner layer, made of VP2, encloses the genomic RNA and two minor proteins, VP1 and VP3, with which it forms the viral core. Core assembly is coupled with RNA viral replication and takes place in definite cellular structures termed viroplasms. Replication and encapsidation mechanisms are still not fully understood, and little information is available about the intermolecular interactions that may exist among the viroplasmic proteins. NSP2 and NSP5 are two nonstructural viroplasmic proteins that have been shown to interact with each other. They have also been found to be associated with precore replication intermediates that are precursors of the viral core. In this study, we show that NSP5 interacts with VP2 in infected cells. This interaction was demonstrated with recombinant proteins expressed from baculovirus recombinants or in bacterial systems. NSP5-VP2 interaction also affects the stability of VP6 bound to VP2 assemblies. The data presented showed evidence, for the first time, of an interaction between VP2 and a nonstructural rotavirus protein. Published data and the interaction demonstrated here suggest a possible role for NSP5 as an adapter between NSP2 and the replication complex VP2-VP1-VP3 in core assembly and RNA encapsidation, modulating the role of NSP2 as a molecular motor involved in the packaging of viral mRNA.

Mitochondrial permeability transition as a novel principle of hepatorenal toxicity in vivo

Atractyloside (Atr) binds to the adenine nucleotide translocator (ANT) and inhibits ANT-mediated ATP/ADP exchange on the inner mitochondrial membrane. In addition, Atr can trigger opening of a non-specific ion channel, within the ANT-containing permeability transition pore complex (PTPC), which is subject to redox regulation and inhibited by cyclosporin A (CsA). Here we show that the cytotoxic effects of Atr, both in vivo and in vitro, are determined by its capacity to induce PTPC opening and consequent mitochondrial membrane permeabilization (MMP). Thus, the Atr-induced MMP and death of cultured liver cells are both inhibited by CsA as well as by glutathione (GSH) and enhanced by GSH depletion. Similarly, the hepatorenal toxicity of Atr, assessed in vivo, was reduced by treating mice with CsA or a diet rich in sulfur amino acids, a regime which enhances mitochondrial GSH levels. Atr injection induced MMP in hepatocytes and proximal renal tubular cells, and MMP was reduced by either CsA or GSH. Acetaminophen (paracetamol)-induced acute poisoning was also attenuated by CsA and GSH, both in vitro and in vivo. Altogether these data indicate that PTPC-mediated MMP may determine the hepatorenal toxicity of xenobiotics in vivo.

A human rotavirus with rearranged genes 7 and 11 encodes a modified NSP3 protein and suggests an additional mechanism for gene rearrangement

A human rotavirus (isolate M) with an atypical electropherotype with 14 apparent bands of double-stranded RNA was isolated from a chronically infected immunodeficient child. MA-104 cell culture adaptation showed that the M isolate was a mixture of viruses containing standard genes (M0) or rearranged genes: M1 (containing a rearranged gene 7) and M2 (containing rearranged genes 7 and 11). The rearranged gene 7 of virus M1 (gene 7R) was very unusual because it contained two complete open reading frames (ORF). Moreover, serial propagation of virus M1 in cell culture indicated that gene 7R rapidly evolved, leading to a virus with a deleted gene 7R (gene 7RDelta). Gene 7RDelta coded for a modified NSP3 protein (NSP3m) of 599 amino acids (aa) containing a repetition of aa 8 to 296. The virus M3 (containing gene 7RDelta) was not defective in cell culture and actually produced NSP3m. The rearranged gene 11 (gene 11R) had a more usual pattern, with a partial duplication leading to a normal ORF followed by a long 3' untranslated region. The rearrangement in gene 11R was almost identical to some of those previously described, suggesting that there is a hot spot for gene rearrangements at a specific location on the sequence. It has been suggested that in some cases the existence of short direct repeats could favor the occurrence of rearrangement at a specific site. The computer modeling of gene 7 and 11 mRNAs led us to propose a new mechanism for gene rearrangements in which secondary structures, besides short direct repeats, might facilitate and direct the transfer of the RNA polymerase from the 5' to the 3' end of the plus-strand RNA template during the replication step.

Cap-Poly(A) synergy in mammalian cell-free extracts. Investigation of the requirements for poly(A)-mediated stimulation of translation initiation

The 5' cap and 3' poly(A) tail of eukaryotic mRNAs cooperate to stimulate synergistically translation initiation in vivo, a phenomenon observed to date in vitro only in translation systems containing endogenous competitor mRNAs. Here we describe nuclease-treated rabbit reticulocyte lysates and HeLa cell cytoplasmic extracts that reproduce cap-poly(A) synergy in the absence of such competitor RNAs. Extracts were rendered poly(A)-dependent by ultracentrifugation to partially deplete them of ribosomes and associated initiation factors. Under optimal conditions, values for synergy in reticulocyte lysates approached 10-fold. By using this system, we investigated the molecular mechanism of poly(A) stimulation of translation. Maximal cap-poly(A) cooperativity required the integrity of the eukaryotic initiation factor 4G-poly(A)-binding protein (eIF4G-PABP) interaction, suggesting that synergy results from mRNA circularization. In addition, polyadenylation stimulated uncapped cellular mRNA translation and that driven by the encephalomyocarditis virus internal ribosome entry segment (IRES). These effects of poly(A) were also sensitive to disruption of the eIF4G-PABP interaction, suggesting that 5'-3' end cross-talk is functionally conserved between classical mRNAs and an IRES-containing mRNA. Finally, we demonstrate that a rotaviral non-structural protein that evicts PABP from eIF4G is capable of provoking the shut-off of host cell translation seen during rotavirus infection.

Allelic diversity of the two transferrin binding protein B gene isotypes among a collection of Neisseria meningitidis strains representative of serogroup B disease: implication for the composition of a recombinant TbpB-based vaccine

The distribution of the two isotypes of tbpB in a collection of 108 serogroup B meningococcal strains belonging to the four major clonal groups associated with epidemic and hyperendemic disease (the ET-37 complex, the ET-5 complex, lineage III, and cluster A4) was determined. Isotype I strains (with a 1.8-kb tbpB gene) was less represented than isotype II strains (19.4 versus 80.6%). Isotype I was restricted to the ET-37 complex strains, while isotype II was found in all four clonal complexes. The extent of the allelic diversity of tbpB in these two groups was studied by PCR restriction analysis and sequencing of 10 new tbpB genes. Four major tbpB gene variants were characterized: B16B6 (representative of isotype I) and M982, BZ83, and 8680 (representative of isotype II). The relevance of these variants was assessed at the antigenic level by the determination of cross-bactericidal activity of purified immunoglobulin G preparations raised to the corresponding recombinant TbpB (rTbpB) protein against a panel of 27 strains (5 of isotype I and 22 of isotype II). The results indicated that rTbpB corresponding to each variant was able to induce cross-bactericidal antibodies. However, the number of strains killed with an anti-rTbpB serum was slightly lower than that obtained with an anti-TbpA(+)B complex. None of the sera tested raised against an isotype I strain was able to kill an isotype II strain and vice versa. None of the specific antisera tested (anti-rTbpB or anti-TbpA(+)B complex) was able to kill all of the 22 isotype II strains tested. Moreover, using sera raised against the C-terminus domain of TbpB M982 (amino acids 352 to 691) or BZ83 (amino acids 329 to 669) fused to the maltose-binding protein, cross-bactericidal activity was detected against 12 and 7 isotype II strains, respectively, of the 22 tested. These results suggest surface accessibility of the C-terminal end of TbpB. Altogether, these results show that although more than one rTbpB will be required in the composition of a TbpB-based vaccine to achieve a fully cross-bactericidal activity, rTbpB and its C terminus were able by themselves to induce cross-bactericidal antibodies.

Efficient translation of rotavirus mRNA requires simultaneous interaction of NSP3 with the eukaryotic translation initiation factor eIF4G and the mRNA 3' end

In contrast to the vast majority of cellular proteins, rotavirus proteins are translated from capped but nonpolyadenylated mRNAs. The viral nonstructural protein NSP3 specifically binds the 3'-end consensus sequence of viral mRNAs and interacts with the eukaryotic translation initiation factor eIF4G. Here we show that expression of NSP3 in mammalian cells allows the efficient translation of virus-like mRNA. A synergistic effect between the cap structure and the 3' end of rotavirus mRNA was observed in NSP3-expressing cells. The enhancement of viral mRNA translation by NSP3 was also observed in a rabbit reticulocyte lysate translation system supplemented with recombinant NSP3. The use of NSP3 mutants indicates that its RNA- and eIF4G-binding domains are both required to enhance the translation of viral mRNA. The results reported here show that NSP3 forms a link between viral mRNA and the cellular translation machinery and hence is a functional analogue of cellular poly(A)-binding protein.

Cleavage of polypeptide chain initiation factor eIF4GI during apoptosis in lymphoma cells: characterisation of an internal fragment generated by caspase-3-mediated cleavage

Polypeptide chain initiation factor eIF4GI undergoes caspase-mediated degradation during apoptosis to give characteristic fragments. The most prominent of these has an estimated mass of approximately 76 kDa (Middle-Fragment of Apoptotic cleavage of eIF4G; M-FAG). Subcellular fractionation of the BJAB lymphoma cell line after induction of apoptosis indicates that M-FAG occurs in both ribosome-bound and soluble forms. Affinity chromatography on m7GTP-Sepharose shows that M-FAG retains the ability of eIF4GI to associate with both the mRNA cap-binding protein eIF4E and initiation factor eIF4A and that the ribosome-bound form of M-FAG is also present as a complex with eIF4E and eIF4A. These data suggest that the binding sites for eIF4E, eIF4A and eIF3 on eIF4GI are retained in the caspase-generated fragment. M-FAG is also a substrate for cleavage by the Foot-and-Mouth-Disease Virus-encoded L protease. These properties, together with the pattern of recognition by a panel of antibodies, define the origin of the apoptotic cleavage fragment. N-terminal sequencing of the products of caspase-3-mediated eIF4GI cleavage has identified the major cleavage sites. The pattern of eIF4GI degradation and the possible roles of the individual cleavage products in cells undergoing apoptosis are discussed.

The viral nucleocapsid protein of transmissible gastroenteritis coronavirus (TGEV) is cleaved by caspase-6 and -7 during TGEV-induced apoptosis

The transmissible gastroenteritis coronavirus (TGEV), like many other viruses, exerts much of its cytopathic effect through the induction of apoptosis of its host cell. Apoptosis is coordinated by a family of cysteine proteases, called caspases, that are activated during apoptosis and participate in dismantling the cell by cleaving key structural and regulatory proteins. We have explored the caspase activation events that are initiated upon infection of the human rectal tumor cell line HRT18 with TGEV. We show that TGEV infection results in the activation of caspase-3, -6, -7, -8, and -9 and cleavage of the caspase substrates eIF4GI, gelsolin, and alpha-fodrin. Surprisingly, the TGEV nucleoprotein (N) underwent proteolysis in parallel with the activation of caspases within the host cell. Cleavage of the N protein was inhibited by cell-permeative caspase inhibitors, suggesting that this viral structural protein is a target for host cell caspases. We show that the TGEV nucleoprotein is a substrate for both caspase-6 and -7, and using site-directed mutagenesis, we have mapped the cleavage site to VVPD(359) downward arrow. These data demonstrate that viral proteins can be targeted for destruction by the host cell death machinery.

The C-terminal domain of rotavirus NSP5 is essential for its multimerization, hyperphosphorylation and interaction with NSP6

Rotavirus NSP5 is a non-structural phosphoprotein with putative autocatalytic kinase activity, and is present in infected cells as various isoforms having molecular masses of 26, 28 and 30-34 kDa. We have previously shown that NSP5 forms oligomers and interacts with NSP6 in yeast cells. Here we have mapped the domains of NSP5 responsible for these associations. Deletion mutants of the rotavirus YM NSP5 were constructed and assayed for their ability to interact with full-length NSP5 and NSP6 using the yeast two-hybrid assay. The homomultimerization domain was mapped to the 20 C-terminal aa of the protein, which have a predicted alpha-helical structure. A deletion mutant lacking the 10 C-terminal aa (DeltaC10) failed to multimerize both in yeast cells and in an in vitro affinity assay. When transiently expressed in MA104 cells, NSP5 became hyperphosphorylated (30-34 kDa isoforms). In contrast, the DeltaC10 mutant produced forms equivalent to the 26 and 28 kDa species, but was poorly hyperphosphorylated, suggesting that multimerization is important for this proposed activity of the protein. The interaction domain with NSP6 was found to be present in the 35 C-terminal aa of NSP5, overlapping the multimerization domain of the protein, and suggesting that NSP6 might have a regulatory role in the self-association of NSP5. NSP6 was also found to interact with wild-type NSP5, but not with its mutant DeltaC10, in cells transiently transfected with plasmids encoding these proteins, confirming the relevance of the 10 C-terminal aa for the formation of the heterocomplex.

Identification of the RNA-binding, dimerization, and eIF4GI-binding domains of rotavirus nonstructural protein NSP3

The rotavirus nonstructural protein NSP3 is a sequence-specific RNA binding protein that binds the nonpolyadenylated 3' end of the rotavirus mRNAs. NSP3 also interacts with the translation initiation factor eIF4GI and competes with the poly(A) binding protein. Deletion mutations and point mutations of NSP3 from group A rotavirus (NSP3A), expressed in Escherichia coli, indicate that the RNA binding domain lies between amino acids 4 and 149. Similar results were obtained with NSP3 from group C rotaviruses. Data also indicate that a dimer of NSP3A binds one molecule of RNA and that dimerization is necessary for strong RNA binding. The dimerization domain of NSP3 was mapped between amino acids 150 and 206 by using the yeast two-hybrid system. The eukaryotic initiation factor 4 GI subunit (eIF-4GI) binding domain of NSP3A has been mapped in the last 107 amino acids of its C terminus by using a pulldown assay and the yeast two-hybrid system. NSP3 is composed of two functional domains separated by a dimerization domain.

Both the full-length and the N-terminal domain of the meningococcal transferrin-binding protein B discriminate between human iron-loaded and apo-transferrin

We have readdressed the ability of the transferrin-binding protein B (TbpB) from Neisseria meningitidis to discriminate between the iron-loaded and the iron-free human transferrin (hTf) by using the BIAcore technology, a powerful experimental technique for the observation of direct interactions between a receptor and its ligands, without the use of labels. Recombinant full-length TbpB from five N. meningitidis strains were produced and purified from Escherichia coli as fusion proteins. They showed a preference for the binding to iron-loaded hTf. As for the full-length molecule, we have demonstrated that the minimal N-terminal hTf binding domain of meningococcal TbpB from B16B6 and M982 strains was able to discriminate between both hTf forms.

Rotavirus RNA-binding protein NSP3 interacts with eIF4GI and evicts the poly(A) binding protein from eIF4F

Most eukaryotic mRNAs contain a 5'cap structure and a 3'poly(A) sequence that synergistically increase the efficiency of translation. Rotavirus mRNAs are capped, but lack poly(A) sequences. During rotavirus infection, the viral protein NSP3A is bound to the viral mRNAs 3' end. We looked for cellular proteins that could interact with NSP3A, using the two-hybrid system in yeast. Screening a CV1 cell cDNA library allowed us to isolate a partial cDNA of the human eukaryotic initiation factor 4GI (eIF4GI). The interaction of NSP3A with eIF4GI was confirmed in rotavirus infected cells by co-immunoprecipitation and in vitro with NSP3A produced in Escherichia coli. In addition, we show that the amount of poly(A) binding protein (PABP) present in eIF4F complexes decreases during rotavirus infection, even though eIF4A and eIF4E remain unaffected. PABP is removed from the eIF4F complex after incubation in vitro with the C-terminal part of NSP3A, but not with its N-terminal part produced in E.coli. These results show that a physical link between the 5' and the 3' ends of mRNA is necessary for the efficient translation of viral mRNAs and strongly support the closed loop model for the initiation of translation. These results also suggest that NSP3A, by taking the place of PABP on eIF4GI, is responsible for the shut-off of cellular protein synthesis.

Identification of human transferrin-binding sites within meningococcal transferrin-binding protein B

Transferrin-binding protein B (TbpB) from Neisseria meningitidis binds human transferrin (hTf) at the surface of the bacterial cell as part of the iron uptake process. To identify hTf binding sites within the meningococcal TbpB, defined regions of the molecule were produced in Escherichia coli by a translational fusion expression system and the ability of the recombinant proteins (rTbpB) to bind peroxidase-conjugated hTf was characterized by Western blot and dot blot assays. Both the N-terminal domain (amino acids [aa] 2 to 351) and the C-terminal domain (aa 352 to 691) were able to bind hTf, and by a peptide spot synthesis approach, two and five hTf binding sites were identified in the N- and C-terminal domains, respectively. The hTf binding activity of three rTbpB deletion variants constructed within the central region (aa 346 to 543) highlighted the importance of a specific peptide (aa 377 to 394) in the ligand interaction. Taken together, the results indicated that the N- and C-terminal domains bound hTf approximately 10 and 1000 times less, respectively, than the full-length rTbpB (aa 2 to 691), while the central region (aa 346 to 543) had a binding avidity in the same order of magnitude as the C-terminal domain. In contrast with the hTf binding in the N-terminal domain, which was mediated by conformational epitopes, linear determinants seemed to be involved in the hTf binding in the C-terminal domain. The host specificity for transferrin appeared to be mediated by the N-terminal domain of the meningococcal rTbpB rather than the C-terminal domain, since we report that murine Tf binds to the C-terminal domain. Antisera raised to both N- and C-terminal domains were bactericidal for the parent strain, indicating that both domains are accessible at the bacterial surface. We have thus identified hTf binding sites within each domain of the TbpB from N. meningitidis and propose that the N- and C-terminal domains together contribute to the efficient binding of TbpB to hTf with their respective affinities and specificities for determinants of their ligand.

Two proline residues are essential in the calcium-binding activity of rotavirus VP7 outer capsid protein

Rotavirus maturation and stability of the outer capsid are calcium-dependent processes. It has been shown previously that the concentration of Ca2+-solubilizing outer capsid proteins from rotavirus particles is dependent on the virus strain. This property of viral particles has been associated with the gene coding for VP7 (gene 9). In this study the correlation between VP7 and resistance to low [Ca2+] was confirmed by analyzing the origin of gene 9 from reassortant viruses prepared under the selective pressure of low [Ca2+]. After chemical mutagenesis, we selected mutant viruses of the bovine strain RF that are more resistant to low [Ca2+]. The genes coding for the VP7 proteins of these independent mutants have been sequenced. Sequence analysis confirmed that these mutants are independent and revealed that all mutant VP7 proteins have proline 75 changed to leucine and have an outer capsid that solubilized at low [Ca2+]. The mutation of proline 279 to serine is found in all but two mutants. The phenotype of mutants having a single proline change can be distinguished from the phenotype of mutants having two proline changes. Sequence analysis showed that position 75 is in a region (amino acids 65 to 78) of great variability and that proline 75 is present in most of the bovine strains. In contrast, proline 279 is in a conserved region and is conserved in all the VP7 sequences in data banks. This region is rich in oxygenated residues that are correctly allocated in the metal-coordinating positions of the Ca2+-binding EF-hand structure pattern, suggesting that this region is important in the Ca2+ binding of VP7.

In vivo and in vitro phosphorylation of rotavirus NSP5 correlates with its localization in viroplasms

NSP5 (NS26), the product of rotavirus gene 11, is a phosphoprotein whose role in the virus replication cycle is unknown. To gain further insight into its function, we obtained monoclonal antibodies against the baculovirus-expressed protein. By immunoprecipitation and immunoblotting experiments, we showed that (i) NSP5 appears in many different phosphorylated forms in rotavirus-infected cells; (ii) immunoprecipitated NSP5 from rotavirus-infected cells can be phosphorylated in vitro by incubation with ATP; (iii) NSP5, produced either by transient transfection of rotavirus gene 11 or by infection by gene 11 recombinant vaccinia virus or baculovirus, can be phosphorylated in vivo and in vitro; (iv) NSP5 expressed in Escherichia coli is phosphorylated in vitro, and thus NSP5 is a potential protein kinase; and (v) NSP5 forms dimers and interacts with NSP2. The intracellular localization of NSP5 in the course of rotavirus infection and after transient expression in COS7 cells has also been investigated. In rotavirus-infected cells, NSP5 is localized in viroplasms, but it is widespread throughout the cytoplasm of transfected COS7 cells. NSP5 produced by transfected COS7 cells did not acquire the multiphosphorylated forms observed in rotavirus-infected COS7 cells. Thus, there is a tight correlation between the localization of NSP5 in the viroplasms and its protein kinase activity in vivo or in vitro. Our results suggest that cellular or viral cofactors are indispensable to fully phosphorylate NSP5 and to reach its intracellular localization.

Recovery and characterization of a replicase complex in rotavirus-infected cells by using a monoclonal antibody against NSP2

Replication of the rotavirus genome involves two steps: (i) transcription and extrusion of transcripts and (ii) minus-strand RNA synthesis in viral complexes containing plus-strand RNA. In this study, we showed evidence for the importance of the viral nonstructural protein of rotavirus, NSP2, in the replication of viral RNAs. RNA-binding properties of NSP2 were tested by UV cross-linking in vivo (in rotavirus-infected MA104 cells and recombinant baculovirus-expressing NSP2-infected Sf9 cells). In rotavirus-infected cells, NSP2 is bound to the 11 double-stranded RNA genomic segments of rotavirus. Quantitative analysis (using hydrolysis by RNase A) is consistent with NSP2 being directly bound to partially replicated viral RNA. Using various monoclonal antibodies and specific antisera against the structural (VP1, VP2, and VP6) and nonstructural (NSP1, NSP2, NSP3, and NSP5) proteins, we developed a solid-phase assay for the viral replicase. In this test, we recovered a viral RNA-protein complex with replicase activity only with a monoclonal antibody directed against NSP2. Our results indicated that these viral complexes contain the structural proteins VP1, VP2, and VP6 and the nonstructural protein NSP2. Our results show that NSP2 is closely associated in vivo with the viral replicase.

Structure and function of rotavirus nonstructural protein NSP3

The genomes of viruses in the family Reoviridae consist of segmented double-stranded RNA. There are 10 to 12 segments depending on the genus. The 5' ends and the 3' ends of the RNAs present conserved motifs for each virus genus. These conserved motifs have been hypothesized to play a role in genomic segment assortment during virus morphogenesis. Using a set of monoclonal antibodies we have tried to identify rotaviral proteins that bind to RNA during infection in cell culture. This methodology takes advantage of being able to label RNA in vitro to high specific activity and also of solid phase processing of RNA-protein complexes. After cross-linking the RNA to protein in infected cells, protein-RNA complexes are precipitated with a specific MAb; then, the RNA in the complex is labeled in vitro and the protein or nucleic acid moieties are analyzed by usual protocols. This paper describes results using an anti NSP3 MAb. In infected cells, we have shown that NSP3 binds to the eleven messenger RNAs, and that a sequence from nucleotides 8 to 15 is protected from digestion with RNAse T1 by NSP3 in the RNA-protein complex. The availability of recombinant protein NSP3 expressed in the baculovirus-insect cell system has allowed the sequence specificity of NSP3 to be studied in vitro. The minimal sequence recognized by NSP3 is GACC. The role of NSP3 in rotavirus replication is discussed based on these results and by comparison with other RNA-binding proteins of members of the Reoviridae family.

Identification of the nucleic acid binding domain of the rotavirus VP2 protein

The bovine rotavirus VP2 protein is the major component of the core and forms the most internal layer surrounding the dsRNA genome. We have constructed recombinant baculoviruses expressing truncated VP2 proteins. The nucleic acid binding activity of these truncated proteins was tested by North-Western blotting experiments with single-stranded and double-stranded probes. The nucleic acid binding domain in VP2 was localized between amino acids 1 to 132. Recombinant proteins bound single-stranded and double-stranded nucleic acids, but showed less affinity for double-stranded RNA and DNA. Interactions of VP2 with the genome were investigated in viral single-shelled particles by u.v.-cross-linking. In these experiments, only VP2 protein bound the genomic RNA in purified single-shelled particles.

Four nucleotides are the minimal requirement for RNA recognition by rotavirus non-structural protein NSP3

The interaction of the group A rotavirus non-structural protein NSP3 (NSP3A) with RNA has been studied in vitro. Using semi-purified NSP3A protein expressed by a recombinant baculovirus and in vitro synthesized RNA, we determined by UV cross-linking and gel retardation assays that NSP3A binds, in a sequence-specific manner, the consensus sequence (AUGUGACC) present on the 3' ends of all group A rotavirus mRNAs. Using short oligoribonucleotides, we established that the minimal RNA sequence required for binding of NSP3A is GACC. Modifications of the UGACC oligonucleotide sequence impaired binding of the protein to the RNA. Furthermore, the recombinant NSP3 protein from rotavirus group C showed specificity for the 3' end consensus sequence (AUGUGGCU) of only group C mRNAs. Sequence analysis of the NSP3 proteins did not reveal significant homologies with other RNA binding proteins, thus the NSP3 proteins of rotaviruses are the prototypes of a new kind of sequence-specific RNA binding protein.

An immunodominant cytotoxic T cell epitope on the VP7 rotavirus protein overlaps the H2 signal peptide

C57BL/6 (H-2b) mice were primed with the bovine RF strain of rotavirus to study the induction of CD8+ cytotoxic T lymphocytes (CTLs). These rotavirus-specific CTLs were detected only after in vitro restimulation with the virus. Using a recombinant vaccinia virus we identified the RF VP7 protein as a major target of these CTLs. The response against this protein was obtained also after in vitro restimulation with simian SA11 and human WA strains of rotavirus. Using published Db and Kb allele-specific motifs to predict possible CTL epitopes in the RF VP7 protein, we synthesized and tested 18 predicted peptides of VP7. Only one peptide was able to sensitize target cells at a concentration below 5 x 10(-7) M. This CTL epitope was also induced by immunization with the RF VP7 expressed with a baculovirus vector, and was shown to be immunodominant by its capacity to inhibit, in an unlabelled target assay, the bulk response against cells infected with recombinant vaccinia virus expressing VP7. This CTL epitope overlaps the H2 signal peptide of the protein.

Rotavirus protein NSP3 (NS34) is bound to the 3' end consensus sequence of viral mRNAs in infected cells

Interaction between viral proteins and RNAs has been studied in rotavirus-infected cells. The use of UV cross-linking followed by immunoprecipitation and labeling with T4 polynucleotide kinase allowed us to detect interactions between RNA and nonstructural viral proteins. The RNAs linked to the nonstructural protein NSP3 have been identified as rotavirus mRNAs, and the sequences of the RNase T1-protected fragments have been established. These sequences correspond to the 3' end sequence common to all rotavirus group A genes. We also show that the last 3' nucleotide is cross-linked to the protein and that monomeric and multimeric forms of NSP3 are bound to rotavirus mRNA. The role of NSP3 in rotavirus replication is discussed in the light of our results and by comparison with other RNA-binding proteins of members of the Reoviridae family.

Inhibition of proliferation of primary avian fibroblasts through expression of histone H5 depends on the degree of phosphorylation of the protein

To obtain stable and constitutive expression of histone H5 at levels comparable to those observed in normal chicken erythrocytes, an avian self-inactivating retroviral vector was used to transfer the H5 gene into cells which do not express this protein. The vector, pDAH5, was obtained by removing the CAAT and TATA boxes of the 3'LTR of the avian leukosis virus RAV-2 and inserting the H5 sequence. Infection of QT6 quail cells with the recombinant virus (DAH5) led to the stable integration of the foreign H5 gene at low copy number, to the formation of correctly initiated mRNA transcripts and to the production of H5 protein. The amount of H5 expressed was equivalent to that of a mature chicken erythrocyte. Expression of histone H5 in DAH5 transformed cells, such as QT6 or AEV-ES4, transformed chicken embryo fibroblasts had only slight effects on the growth rate and did not inhibit cell replication. Conversely, the effect of H5 expression on normal quail and chicken fibroblasts was dramatic: cells acquired the aspect of quiescent fibroblasts, grew very slowly, and nuclei looked compacted, often extruded from the cell. The H5 histone produced in QT6-transformed cells was found to be phosphorylated while in normal chicken fibroblasts the protein lacked this posttranslational modification. It is proposed that the chromatin-condensing role of histone H5 is inhibited by its phosphorylation.

Sequences in rotavirus glycoprotein VP7 that mediate delayed translocation and retention of the protein in the endoplasmic reticulum

Glycosylation and translocation of the simian rotavirus protein VP7, a resident ER protein, does not occur co-translationally in vivo. In pulse-chase experiments in COS cells, nonglycosylated VP7 was still detectable after a 25-min chase period, although the single glycosylation site was only 18 residues beyond the signal peptide cleavage site. After labeling, glycosylated and nonglycosylated VP7 was recovered in microsomes but the latter was sensitive to trypsin (i.e., the nascent protein became membrane associated) but most of it entered the ER posttranslationally because of a rate-limiting step early in translocation. In contrast with the simian protein, bovine VP7 was glycosylated and translocated rapidly. Thus, delayed translocation per se was not required for retention of VP7 in the ER. By constructing hybrid proteins, it was further shown that the signal peptide together with residues 64-111 of the simian protein caused delayed translocation. The same sequences were also necessary and sufficient for retention of simian VP7 in the ER. The data are consistent with the idea that certain proteins are inserted into the ER membrane in a loop configuration.

A recombinant vaccinia virus expressing the major capsid protein of Simian rotavirus-induced anti-rotavirus antibodies

cDNA molecules encoding the major structural protein (VP6) of the Simian rotavirus SA11 were inserted under the control of the vaccinia virus 7.5 kDa promoter into the thymidine kinase gene. Synthesis of VP6 was demonstrated by immunoprecipitation of recombinant virus-infected cell. Mice inoculated via several routes with this recombinant vaccinia produce high titers of antirotavirus antibodies lacking neutralizing activity.

A plaque hybridization assay for rotaviruses

A plaque hybridization assay was adapted to rotavirus. In this test cDNA or oligonucleotide probes were used to discriminate between plaques originating from virus carrying genes of bovine and simian origin. Only mRNAs present in infected cells were detected as demonstrated by using oligonucleotides corresponding to both strands. This assay can be used to screen reassortants or mutants of rotaviruses.

Generation of a helper cell line for packaging avian leukosis virus-based vectors

We constructed an avian leukosis virus-based packaging cell line, pHF-g, containing Rous-associated virus DNA with several alterations to abolish RNA packaging. One of them is a 52-base-pair deletion encompassing the putative encapsidation signal in the leader region. The 3' long terminal repeat was also removed and replaced by the polyadenylation sequence from the herpes simplex virus thymidine kinase gene. When pHF-g cells were transfected by an avian leukosis virus-based vector, they produced replication-defective virus at high titer but they did not release any replication-competent particles. Proviral DNA was shown to be correctly integrated as well as correctly expressed. Viral RNAs were shown to be correctly translated into gag-related polypeptides.

A new method for detection of small modifications in genomic DNA, applied to the human delta-beta globin gene cluster

Cloned DNA fragments were subcloned in filamentous coliphages fd 103 or M 13; the recombinant single-stranded DNAs were then used to form hybrids with genomic DNA as well as with complementary recombinant single-stranded DNA. Hybrids were submitted to S1-nuclease treatment alone or in combination with restriction enzyme digestions. This method was used to analyze the delta-beta globin gene cluster from the total genomic DNA of a beta 0-thalassemic patient. A modification located approximately 530 base pairs upstream from the cap site of the beta-globin gene was detected in only one thalassemic chromosome of this patient. Sequence analysis have shown that the patient was homozygous for a single nucleoside change (dC----dT) which remains undetected by our hybridization method, leading to a codon 39 nonsense mutation; they have demonstrated too that he was heterozygous for the modification mentioned and detected by S1-nuclease, which corresponds to an additional sequence d(T-A-T-A) in a 52 alternating purine-pyrimidine run, leading to a complex change from d[(A-T)7(T)7] to d[(A-T)11(T)3].

S1-nuclease mapping of the genomic Lepore-Boston DNA demonstrates that the entire large intervening sequence of the fusion gene is of beta-type

Several reports have suggested but not proven that the large intervening sequence of Lepore delta-beta fusion gene was of beta-type (3-5). A method able to detect rearrangements as small as 4 nucleotide pairs directly into genomic DNA (6) has been applied to the total DNA of a heterozygous Lepore-Boston patient in order to identify accurately the origin of the large intervening sequence of the delta-beta fusion-gene. Hybrid duplexes were formed between genomic Lepore DNA and single-stranded DNA used as probes, then submitted to S1-nuclease treatment. Our data demonstrate that the entire large intervening sequence of the Lepore fusion gene is of beta-type. Moreover, no large modification was detected in any delta- and beta parts of the delta-beta fusion gene.

Non-random association of the polymorphic Taq I restriction site, located 3 KB 5' to the human delta-globin gene, with the polymorphic Hind III sites within the G gamma- and A gamma-globin genes

During the study of the DNA from 25 beta-thalassemic subjects from mediterranean origin the polymorphic Taq I restriction site located 3-kb 5' to the human delta-globin gene, was found non-randomly associated to the polymorphic Hind III sites within the G gamma- and A gamma-globin genes. This indicates that the 3' limit of the linkage group of polymorphic restriction sites including the gamma-globin genes is located downstream to the polymorphic Taq I site.

CG sites and their nucleotide environment in the human gamma-delta-beta-globin gene cluster: distribution, frequency and possible frame for differential methylation

Available restriction endonucleases including CG dinucleotides in their target sequences (most of them being unable to cut the DNA when the cytosine of the CG sequence is methylated) have been used to map cloned DNA covering the human gamma-delta-beta globin gene cluster. Since the human DNA fragments were cloned in Escherichia coli, only the internal cytosine in the sequence CCAT GG could be methylated. Thus, any recognized "CG enzyme" site can be detected since they are unmethylated. Results show that frequencies of "CG enzyme" sites regularly decrease from the gamma-globin region to the beta-globin region, the latter being very poor in "CG enzyme"' sites. The array of enzymes used here detects 4 times more CG sites than the classical MspI/HpaII system. Examination of previously sequenced parts of the gamma-delta-beta globin gene cluster shows that CG dinucleotides correspond to an average frequency of 1 out of 104 nucleotides in the gamma-globin region and 1 out of 138 nucleotides in the beta-globin region. In the gamma-globin region, 1 CG out of 4 or 5 may be detected by the enzymes used; the detected frequency is less than 1 out of 10 CG in the beta-region. Analysis of nucleotide environment around CG dinucleotides shows occurrence of local differences, the main sequences being CGG in the 5' side flanking the gamma genes and ACG in the corresponding area of the beta gene. The results presented introduce some new considerations about analysis of cytosine methylation which has been previously proposed as playing a role in the control of the activity of gamma, delta and beta genes respectively.