Separation of ten reovirus genome segments by polyacrylamide gel electrophoresis

Engineering Non-Human RNA Viruses for Cancer Therapy

Alongside the development and progress in cancer immunotherapy, research in oncolytic viruses (OVs) continues advancing novel treatment strategies to the clinic. With almost 50 clinical trials carried out over the last decade, the opportunities for intervention using OVs are expanding beyond the old-fashioned concept of "lytic killers", with promising breakthrough therapeutic strategies focused on leveraging the immunostimulatory potential of different viral platforms. This review presents an overview of non-human-adapted RNA viruses engineered for cancer therapy. Moreover, we describe the diverse strategies employed to manipulate the genomes of these viruses to optimize their therapeutic capabilities. By focusing on different aspects of this particular group of viruses, we describe the insights into the promising advancements in the field of virotherapy and its potential to revolutionize cancer treatment.

Modulation of Reoviral Cytolysis (II): Cellular Stemness

Oncolytic viruses (OVs) are an emerging cancer therapeutic that are intended to act by selectively targeting and lysing cancerous cells and by stimulating anti-tumour immune responses, while leaving normal cells mainly unaffected. Reovirus is a well-studied OV that is undergoing advanced clinical trials and has received FDA approval in selected circumstances. However, the mechanisms governing reoviral selectivity are not well characterised despite many years of effort, including those in our accompanying paper where we characterize pathways that do not consistently modulate reoviral cytolysis. We have earlier shown that reovirus is capable of infecting and lysing both certain types of cancer cells and also cancer stem cells, and here we demonstrate its ability to also infect and kill healthy pluripotent stem cells (PSCs). This led us to hypothesize that pathways responsible for stemness may constitute a novel route for the modulation of reoviral tropism. We find that reovirus is capable of killing both murine and human embryonic and induced pluripotent stem cells. Differentiation of PSCs alters the cells' reoviral-permissive state to a resistant one. In a breast cancer cell line that was resistant to reoviral oncolysis, induction of pluripotency programming rendered the cells permissive to cytolysis. Bioinformatic analysis indicates that expression of the Yamanaka pluripotency factors may be associated with regulating reoviral selectivity. Mechanistic insights from these studies will be useful for the advancement of reoviral oncolytic therapy.

Oncolytic Reoviruses: Can These Emerging Zoonotic Reoviruses Be Tamed and Utilized?

Orthoreovirus is a nonenveloped double-stranded RNA virus under the Reoviridae family. This group of viruses, especially mammalian orthoreovirus (MRV), are reported with great therapeutic values due to their oncolytic effects. In this review, the life cycle and oncolytic effect of MRV and a few emerging reoviruses were summarized. This article also highlights the challenges and strategies of utilizing MRV and the emerging reoviruses, avian orthoreovirus (ARV) and pteropine orthoreovirus (PRV), as oncolytic viruses (OVs). Besides, the emergence of potential ARV and PRV as OVs were discussed in comparison to MRV. Finally, the risk of reovirus as zoonosis or reverse zoonosis (zooanthroponosis) were debated, and concerns were raised in this article, which warrant continue surveillance of reovirus (MRV, ARV, and PRV) in animals, humans, and the environment.

First report on co-isolation and whole-genomic characterisation of mammalian orthorubulavirus 5 and mammalian orthoreovirus type 3 from domestic pigs in India

During a surveillance study to monitor porcine epidemic diarrohoea virus and transmissible gastroenteritis virus in India, a total of 1043 swine samples including faeces (n = 264) and clotted blood (n = 779) were collected and tested. Five samples (four faecal and one serum) showed cytopathic effects in Vero cells. Transmission electron microscopy of infectious cell supernatant revealed the presence of two types of virions. Next-generation sequencing (de novo) allowed the complete genome sequence of mammalian orthorubulavirus 5 (MRuV5; 15246 bp) and that of all 10 gene segments of mammalian orthoreovirus to be determined. Genetic analysis of MRuV5 revealed grouping of the Indian MRuV5 with isolates from various mammalian species in South Korea and China, sharing more than 99% nucleotide sequence identity. The deduced amino acid sequences of the HN, NP, and F genes of MRuV5 isolates showed three (92L, 111R, 447H), two (86S, 121S), and two (139T, 246T) amino acid substitutions, respectively, compared to previously reported virus strains. Phylogenic analysis based on S1 gene sequences showed the Indian MRV isolates to be clustered in lineage IV of MRV type 3, with the highest nucleotide sequence identity (97.73%) to MRV3 strain ZJ2013, isolated from pigs in China. The protein encoded by the MRV3 S1 gene was found to contain the amino acid residues 198-204NLAIRLP, 249I, 340D, and 419E, which are known to be involved in sialic acid binding and neurotropism. This is the first report of co-isolation and whole-genomic characterisation of MRuV5 and MRV3 in domestic pigs in India. The present study lays a foundation for further surveillance studies and continuous monitoring of the emergence and spread of evolving viruses that might have pathogenic potential in animal and human hosts.

Engineering strategies to enhance oncolytic viruses in cancer immunotherapy

Oncolytic viruses (OVs) are emerging as potentially useful platforms in treatment methods for patients with tumors. They preferentially target and kill tumor cells, leaving healthy cells unharmed. In addition to direct oncolysis, the essential and attractive aspect of oncolytic virotherapy is based on the intrinsic induction of both innate and adaptive immune responses. To further augment this efficacious response, OVs have been genetically engineered to express immune regulators that enhance or restore antitumor immunity. Recently, combinations of OVs with other immunotherapies, such as immune checkpoint inhibitors (ICIs), chimeric antigen receptors (CARs), antigen-specific T-cell receptors (TCRs) and autologous tumor-infiltrating lymphocytes (TILs), have led to promising progress in cancer treatment. This review summarizes the intrinsic mechanisms of OVs, describes the optimization strategies for using armed OVs to enhance the effects of antitumor immunity and highlights rational combinations of OVs with other immunotherapies in recent preclinical and clinical studies.

Asymmetric reconstruction of mammalian reovirus reveals interactions among RNA, transcriptional factor µ2 and capsid proteins

Mammalian reovirus (MRV) is the prototypical member of genus Orthoreovirus of family Reoviridae. However, lacking high-resolution structures of its RNA polymerase cofactor μ2 and infectious particle, limits understanding of molecular interactions among proteins and RNA, and their contributions to virion assembly and RNA transcription. Here, we report the 3.3 Å-resolution asymmetric reconstruction of transcribing MRV and in situ atomic models of its capsid proteins, the asymmetrically attached RNA-dependent RNA polymerase (RdRp) λ3, and RdRp-bound nucleoside triphosphatase μ2 with a unique RNA-binding domain. We reveal molecular interactions among virion proteins and genomic and messenger RNA. Polymerase complexes in three Spinoreovirinae subfamily members are organized with different pseudo-D_3d symmetries to engage their highly diversified genomes. The above interactions and those between symmetry-mismatched receptor-binding σ1 trimers and RNA-capping λ2 pentamers balance competing needs of capsid assembly, external protein removal, and allosteric triggering of endogenous RNA transcription, before, during and after infection, respectively.

Mammalian reovirus (MRV) is a double-stranded RNA (dsRNA) virus that affects the gastrointestinal and respiratory tracts. Here, the authors present the 3.3 Å cryo-EM asymmetric reconstruction of transcribing MRV that reveals the organization of the dsRNA genome, RNA interaction with the polymerase complex, and how the polymerase interacts extensively with its co-factor, µ2, to form a transcription enzyme complex, which engages and regulates RNA transcription.

Reovirus Low-Density Particles Package Cellular RNA

Packaging of segmented, double-stranded RNA viral genomes requires coordination of viral proteins and RNA segments. For mammalian orthoreovirus (reovirus), evidence suggests either all ten or zero viral RNA segments are simultaneously packaged in a highly coordinated process hypothesized to exclude host RNA. Accordingly, reovirus generates genome-containing virions and “genomeless” top component particles. Whether reovirus virions or top component particles package host RNA is unknown. To gain insight into reovirus packaging potential and mechanisms, we employed next-generation RNA-sequencing to define the RNA content of enriched reovirus particles. Reovirus virions exclusively packaged viral double-stranded RNA. In contrast, reovirus top component particles contained similar proportions but reduced amounts of viral double-stranded RNA and were selectively enriched for numerous host RNA species, especially short, non-polyadenylated transcripts. Host RNA selection was not dependent on RNA abundance in the cell, and specifically enriched host RNAs varied for two reovirus strains and were not selected solely by the viral RNA polymerase. Collectively, these findings indicate that genome packaging into reovirus virions is exquisitely selective, while incorporation of host RNAs into top component particles is differentially selective and may contribute to or result from inefficient viral RNA packaging.

Past, Present and Future of Oncolytic Reovirus

Oncolytic virotherapy (OVT) has received significant attention in recent years, especially since the approval of talimogene Laherparepvec (T-VEC) in 2015 by the Food and Drug administration (FDA). Mechanistic studies of oncolytic viruses (OVs) have revealed that most, if not all, OVs induce direct oncolysis and stimulate innate and adaptive anti-tumour immunity. With the advancement of tumour modelling, allowing characterisation of the effects of tumour microenvironment (TME) components and identification of the cellular mechanisms required for cell death (both direct oncolysis and anti-tumour immune responses), it is clear that a "one size fits all" approach is not applicable to all OVs, or indeed the same OV across different tumour types and disease locations. This article will provide an unbiased review of oncolytic reovirus (clinically formulated as pelareorep), including the molecular and cellular requirements for reovirus oncolysis and anti-tumour immunity, reports of pre-clinical efficacy and its overall clinical trajectory. Moreover, as it is now abundantly clear that the true potential of all OVs, including reovirus, will only be reached upon the development of synergistic combination strategies, reovirus combination therapeutics will be discussed, including the limitations and challenges that remain to harness the full potential of this promising therapeutic agent.

Noncanonical Cell Death Induction by Reassortant Reovirus

Triple-negative breast cancer (TNBC) constitutes 10 to 15% of all breast cancer and is associated with worse prognosis than other subtypes of breast cancer. Current therapies are limited to cytotoxic chemotherapy, radiation, and surgery, leaving a need for targeted therapeutics to improve outcomes for TNBC patients. Mammalian orthoreovirus (reovirus) is a nonenveloped, segmented, double-stranded RNA virus in the Reoviridae family. Reovirus preferentially kills transformed cells and is in clinical trials to assess its efficacy against several types of cancer. We previously engineered a reassortant reovirus, r2Reovirus, that infects TNBC cells more efficiently and induces cell death with faster kinetics than parental reoviruses. In this study, we sought to understand the mechanisms by which r2Reovirus induces cell death in TNBC cells. We show that r2Reovirus infection of TNBC cells of a mesenchymal stem-like (MSL) lineage downregulates the mitogen-activated protein kinase/extracellular signal-related kinase pathway and induces nonconventional cell death that is caspase-dependent but caspase 3-independent. Infection of different MSL lineage TNBC cells with r2Reovirus results in caspase 3-dependent cell death. We map the enhanced oncolytic properties of r2Reovirus in TNBC to epistatic interactions between the type 3 Dearing M2 gene segment and type 1 Lang genes. These findings suggest that the genetic composition of the host cell impacts the mechanism of reovirus-induced cell death in TNBC. Together, our data show that understanding host and virus determinants of cell death can identify novel properties and interactions between host and viral gene products that can be exploited for the development of improved viral oncolytics.IMPORTANCE TNBC is unresponsive to hormone therapies, leaving patients afflicted with this disease with limited treatment options. We previously engineered an oncolytic reovirus (r2Reovirus) with enhanced infective and cytotoxic properties in TNBC cells. However, how r2Reovirus promotes TNBC cell death is not known. In this study, we show that reassortant r2Reovirus can promote nonconventional caspase-dependent but caspase 3-independent cell death and that the mechanism of cell death depends on the genetic composition of the host cell. We also map the enhanced oncolytic properties of r2Reovirus in TNBC to interactions between a type 3 M2 gene segment and type 1 genes. Our data show that understanding the interplay between the host cell environment and the genetic composition of oncolytic viruses is crucial for the development of efficacious viral oncolytics.

Polymorphisms in the Most Oncolytic Reovirus Strain Confer Enhanced Cell Attachment, Transcription, and Single-Step Replication Kinetics

Reovirus serotype 3 Dearing (T3D) replicates preferentially in transformed cells and is in clinical trials as a cancer therapy. Laboratory strains of T3D, however, exhibit differences in plaque size on cancer cells and differences in oncolytic activity in vivo This study aimed to determine why the most oncolytic T3D reovirus lab strain, the Patrick Lee laboratory strain (T3D^PL), replicates more efficiently in cancer cells than other commonly used laboratory strains, the Kevin Coombs laboratory strain (T3D^KC) and Terence Dermody laboratory (T3D^TD) strain. In single-step growth curves, T3D^PL titers increased at higher rates and produced ∼9-fold higher burst size. Furthermore, the number of reovirus antigen-positive cells increased more rapidly for T3D^PL than for T3D^TD In conclusion, the most oncolytic T3D^PL possesses replication advantages in a single round of infection. Two specific mechanisms for enhanced infection by T3D^PL were identified. First, T3D^PL exhibited higher cell attachment, which was attributed to a higher proportion of virus particles with insufficient (≤3) σ1 cell attachment proteins. Second, T3D^PL transcribed RNA at rates superior to those of the less oncolytic T3D strains, which is attributed to polymorphisms in M1-encoding μ2 protein, as confirmed in an in vitro transcription assay, and which thus demonstrates that T3D^PL has an inherent transcription advantage that is cell type independent. Accordingly, T3D^PL established rapid onset of viral RNA and protein synthesis, leading to more rapid kinetics of progeny virus production, larger virus burst size, and higher levels of cell death. Together, these results emphasize the importance of paying close attention to genomic divergence between virus laboratory strains and, mechanistically, reveal the importance of the rapid onset of infection for reovirus oncolysis.IMPORTANCE Reovirus serotype 3 Dearing (T3D) is in clinical trials for cancer therapy. Recently, it was discovered that highly related laboratory strains of T3D exhibit large differences in their abilities to replicate in cancer cells in vitro, which correlates with oncolytic activity in a murine model of melanoma. The current study reveals two mechanisms for the enhanced efficiency of T3D^PL in cancer cells. Due to polymorphisms in two viral genes, within the first round of reovirus infection, T3D^PL binds to cells more efficiency and more rapidly produces viral RNAs; this increased rate of infection relative to that of the less oncolytic strains gives T3D^PL a strong inherent advantage that culminates in higher virus production, more cell death, and higher virus spread.

Enhanced Killing of Triple-Negative Breast Cancer Cells by Reassortant Reovirus and Topoisomerase Inhibitors

Breast cancer is the second leading cause of cancer-related deaths in women in the United States. Triple-negative breast cancer constitutes a subset of breast cancer that is associated with higher rates of relapse, decreased survival, and limited therapeutic options for patients afflicted with this type of breast cancer. Mammalian orthoreovirus (reovirus) selectively infects and kills transformed cells, and a serotype 3 reovirus is in clinical trials to assess its efficacy as an oncolytic agent against several cancers. It is unclear if reovirus serotypes differentially infect and kill triple-negative breast cancer cells and if reovirus-induced cytotoxicity of breast cancer cells can be enhanced by modulating the activity of host molecules and pathways. Here, we generated reassortant reoviruses by forward genetics with enhanced infective and cytotoxic properties in triple-negative breast cancer cells. From a high-throughput screen of small-molecule inhibitors, we identified topoisomerase inhibitors as a class of drugs that enhance reovirus infectivity and cytotoxicity of triple-negative breast cancer cells. Treatment of triple-negative breast cancer cells with topoisomerase inhibitors activates DNA damage response pathways, and reovirus infection induces robust production of type III, but not type I, interferon (IFN). Although type I and type III IFNs can activate STAT1 and STAT2, triple-negative breast cancer cellular proliferation is only negatively affected by type I IFN. Together, these data show that reassortant viruses with a novel genetic composition generated by forward genetics in combination with topoisomerase inhibitors more efficiently infect and kill triple-negative breast cancer cells.IMPORTANCE Patients afflicted by triple-negative breast cancer have decreased survival and limited therapeutic options. Reovirus infection results in cell death of a variety of cancers, but it is unknown if different reovirus types lead to triple-negative breast cancer cell death. In this study, we generated two novel reoviruses that more efficiently infect and kill triple-negative breast cancer cells. We show that infection in the presence of DNA-damaging agents enhances infection and triple-negative breast cancer cell killing by reovirus. These data suggest that a combination of a genetically engineered oncolytic reovirus and topoisomerase inhibitors may provide a potent therapeutic option for patients afflicted with triple-negative breast cancer.

Going (Reo)Viral: Factors Promoting Successful Reoviral Oncolytic Infection

Oncolytic viruses show intriguing potential as cancer therapeutic agents. These viruses are capable of selectively targeting and killing cancerous cells while leaving healthy cells largely unaffected. The use of oncolytic viruses for cancer treatments in selected circumstances has recently been approved by the Food and Drug Administration (FDA) of the US and work is progressing on engineering viral vectors for enhanced selectivity, efficacy and safety. However, a better fundamental understanding of tumour and viral biology is essential for the continued advancement of the oncolytic field. This knowledge will not only help to engineer more potent and effective viruses but may also contribute to the identification of biomarkers that can determine which patients will benefit most from this treatment. A mechanistic understanding of the overlapping activity of viral and standard chemotherapeutics will enable the development of better combinational approaches to improve patient outcomes. In this review, we will examine each of the factors that contribute to productive viral infections in cancerous cells versus healthy cells. Special attention will be paid to reovirus as it is a well-studied virus and the only wild-type virus to have received orphan drug designation by the FDA. Although considerable insight into reoviral biology exists, there remain numerous deficiencies in our understanding of the factors regulating its successful oncolytic infection. Here we will discuss what is known to regulate infection as well as speculate about potential new mechanisms that may enhance successful replication. A joint appreciation of both tumour and viral biology will drive innovation for the next generation of reoviral mediated oncolytic therapy.

Detection of mammalian orthoreovirus type-3 (Reo-3) infections in mice based on serotype-specific hemagglutination protein sigma-1

Background

Reovirus type-3 infections cause severe pathologies in young mice and thus influence animal experiments in many ways. Therefore, the Federation of Laboratory Animal Science Associations (FELASA) recommends an annual screening in laboratory mice as part of a thorough health monitoring program. Based on the high protein sequence homology among the different reovirus serotypes, immunofluorescence antibody assay and other indirect methods relying on the whole virus are presumably cross-reactive to antibodies triggered by mammalian orthoreovirus infections independent of the serotype.

Methods

The serotype-specific protein σ-1 was expressed in Escherichia coli with an N-terminal Strep-tag and a C-terminal His-tag. The purified Strep-rσ-1-His-construct was used to develop an indirect ELISA by testing defined positive and negative sera obtained by experimental infection of mice as well as field sera.

Results

The Strep-rσ-1-His-ELISA provided high sensitivity and specificity during validation. Notably, a high selectivity was also observed for sera positively tested for other relevant FELASA-listed pathogens. Screening of field samples indicated that a commercial reovirus type-3-based ELISA might be cross-reactive to other murine reovirus serotypes and thus produces false-positive results.

Conclusions

The prevalence of reovirus type-3 might be overestimated in German animal facilities and most likely in other countries as well. The occurrence of other reovirus serotypes, however, raises the question if murine health monitoring programs should be extended to these pathogens.

Electronic supplementary material

The online version of this article (10.1186/s12985-018-1021-8) contains supplementary material, which is available to authorized users.

Current understanding of reovirus oncolysis mechanisms

Mammalian orthoreovirus (reovirus) is under development as a cancer virotherapy. Clinical trials demonstrate that reovirus-based therapies are safe and tolerated in patients with a wide variety of cancers. Although reovirus monotherapy has proven largely ineffective, reovirus sensitizes cancer cells to existing chemotherapeutic agents and radiation. Clinical trials are underway to test the efficacy of reovirus in combination with chemotherapeutic and radiation regimens and to evaluate the effectiveness of reovirus in conjunction with immunotherapies. Central to the use of reovirus to treat cancer is its capacity to directly kill cancer cells and alter the cellular environment to augment other therapies. Apoptotic cell death is a prominent mechanism of reovirus cancer cell killing. However, reoviruses can also kill cancer cells through nonapoptotic mechanisms. Here, we describe mechanisms of reovirus cancer cell killing, highlight how reovirus is used in combination with existing cancer treatments, and discuss what is known as to how reovirus modulates cancer immunotherapy.

The Orchestra of Reovirus Cell Entry

Purpose of Review

The ability of viruses to infect host cells is dependent on several factors including the availability of cell-surface receptors, antiviral state of cells, and presence of host factors needed for viral replication. Here, we review findings from in vitro and in vivo studies using mammalian orthoreovirus (reovirus) that have identified an intricate group of molecules and mechanisms used by the virus to attach and enter cells.

Recent Findings

Recent findings provide an improved mechanistic understanding of reovirus cell entry. Of special note is the identification of a cellular mediator of cell entry in neuronal and non-neuronal cells, the effect of cell entry on the outcome of infection and cytopathic effects on the host cell, and an improved understanding of the components that promote viral penetration of cellular membranes.

Summary

A mechanistic understanding of the interplay between host and viral factors has enhanced our view of how viruses usurp cellular processes during infection.

Reverse Genetics for Mammalian Orthoreovirus

Reverse genetics allows introduction of specific alterations into a viral genome. Studies performed with mutant viruses generated using reverse genetics approaches have contributed immeasurably to our understanding of viral replication and pathogenesis, and also have led to development of novel vaccines and virus-based vectors. Here, we describe the reverse genetics system that allows for production and recovery of mammalian orthoreovirus, a double-stranded (ds) RNA virus, from plasmids that encode the viral genome.

Novel antiviral effect of lithium chloride on mammalian orthoreoviruses in vitro

Reovirus not only causes considerable economic loss in the swine industry of the United States and other countries, but also threatens the public health due to its zoonotic potential. According to previous reports, LiCl has antiviral activity against a number of viruses. The inhibitory effects of LiCl on reovirus life cycle in Vero cells were evaluated. The unpaired t-test and one-way ANOVA were used to analyze the differences between experimental groups. We first found that LiCl treatment significantly inhibited reovirus replication in a dose-dependent manner. Furthermore, we found that this antiviral activity of LiCl targets the early stage of viral replication. LiCl could be a potential drug against reovirus infection.

Glycan engagement dictates hydrocephalus induction by serotype 1 reovirus

Receptors expressed on the host cell surface adhere viruses to target cells and serve as determinants of viral tropism. Several viruses bind cell surface glycans to facilitate entry, but the contribution of specific glycan moieties to viral disease is incompletely understood. Reovirus provides a tractable experimental model for studies of viral neuropathogenesis. In newborn mice, serotype 1 (T1) reovirus causes hydrocephalus, whereas serotype 3 (T3) reovirus causes encephalitis. T1 and T3 reoviruses engage distinct glycans, suggesting that glycan-binding capacity contributes to these differences in pathogenesis. Using structure-guided mutagenesis, we engineered a mutant T1 reovirus incapable of binding the T1 reovirus-specific glycan receptor, GM2. The mutant virus induced substantially less hydrocephalus than wild-type virus, an effect phenocopied by wild-type virus infection of GM2-deficient mice. In comparison to wild-type virus, yields of mutant virus were diminished in cultured ependymal cells, the cell type that lines the brain ventricles. These findings suggest that GM2 engagement targets reovirus to ependymal cells in mice and illuminate the function of glycan engagement in reovirus serotype-dependent disease.

Receptor utilization strongly influences viral disease, often dictating host range and target cell selection. Different reovirus serotypes bind to different glycans, but a precise function for these molecules in pathogenesis is unknown. We used type 1 (T1) reovirus deficient in binding the GM2 glycan and mice lacking GM2 to pinpoint a role for glycan engagement in hydrocephalus caused by T1 reovirus. This work indicates that engagement of a specific glycan can lead to infection of specific cells in the host and consequent disease at that site. Since reovirus is being developed as a vaccine vector and oncolytic agent, understanding reovirus-glycan interactions may allow manipulation of reovirus glycan-binding properties for therapeutic applications.

Complete genome sequence of a porcine orthoreovirus from southern China

Porcine orthoreoviruses belong to the family Reoviridae and cause mainly mild enteritis in piglets. We present here the complete genome sequence of a novel porcine orthoreovirus strain (GD-1) isolated from a piglet in southern China. Our data will facilitate future investigations of the molecular characteristics and epidemiology of porcine orthoreoviruses.

Molecular epidemiology of group A human rotaviruses in North West region, Cameroon

BACKGROUND

Rotavirus (RV) is the most common cause of severe diarrhea in children <5 years of age worldwide accounting for 527,000 deaths annually. Over 80% of these deaths occur in South Asia and sub-Saharan Africa. RV vaccines have significantly reduced RV-associated morbidity and mortalities in several countries like the United States and Mexico while vaccine trials have proved efficacious in Ghana and other developing countries. However, there is paucity of data on RV infection in Cameroon where diarrhea is a major childhood disease.

METHODS

A total of 534 stool specimens collected between January 2003 and December 2004 from children with acute gastroenteritis in five health districts in the NWR of Cameroon were screened for group A human rotavirus antigen by ELISA and their electropherotypes determined by Polyacrylamide gel electrophoresis.

RESULTS

RV was detected in 153 (28.7%) diarrheic specimens with infection occurring throughout the year, being more common in children under two years of age (P < 0.01) with the highest incidence in the 7-9 months age group (P <0.05). Sub clinical infections (9%) occurred mostly in children aged 0 - 6 months old (P<0.01). Source of drinking water was not associated with RV infection. Eleven electropherotype patterns were detected with predominance of long electropherotypes (92.8%) and mixed electropherotypes were seen only in hospitalized children. Some isolates showed overlapping or merged genome segments 7 and 8 or 9 and presenting with 10 segments of the RV genome.

CONCLUSION

RV is a significant cause of pediatric diarrhea in the NWR affecting mostly children under 2 years of age. Continuous RV surveillance and nationwide surveys are recommended to improve the health of young children in Cameroon. More research is needed to fully characterize the isolated RV strains.

Comparison of the ribonucleic Acid subunits of reovirus, cytoplasmic polyhedrosis virus, and wound tumor virus

Double-stranded ribonucleic acid (RNA) from intact cytoplasmic polynedrosis virus (CPV) and wound tumor virus (WTV) was analyzed by polyacrylamide gel electrophoresis. Using RNA from type 3 reovirus as a standard, it was calculated that CPV-RNA consisted of 9 subunits corresponding to a molecular weight of 12.7 x 10(6) and WTV-RNA consisted of 12 subunits corresponding to a molecular weight of 15.5 x 10(6).

Defective Interference in the Killer System of Saccharomyces cerevisiae

The K(1) killer virus (or plasmid) of Saccharomyces cerevisiae is a noninfectious double-stranded RNA genome found intracellularly packaged in an icosahedral capsid. This genome codes for a protein toxin and for resistance to that toxin. Defective interfering virus mutants are deletion derivatives of the killer virus double-stranded RNA genome; such mutants are called suppressive. Unlike strains carrying the wild-type genome, strains with these deletion derivatives are neither toxin producers nor toxin resistant. If both the suppressive and the wildtype virus are introduced into the same cell, most progeny become toxin-sensitive nonkillers (J. M. Somers, Genetics 74:571-579, 1973). Diploids formed by the mating of a killer with a suppressive strain were grown in liquid culture, and RNA was extracted from samples taken up to 41 generations after the mating. The ratio of killer RNA to suppressive RNA decreased with increasing generations; by 41 generations the killer RNA was barely detectable. The copy numbers of the suppressive genome and its parental killer were virtually the same in isogenic strains, as were the growth rates of diploid strains containing either virus alone. Therefore, suppressiveness, not being due to segregation or overgrowth by faster growing segregants, is likely due to preferential replication or maintenance of the suppressive genome. Three suppressive viruses, all derivatives of the same killer virus (T. K. Sweeney et al., Genetics 84:27-42, 1976), did not coexist stably. The evidence strongly indicates that the largest genome of the three slowly suppressed both of the smaller genomes, showing that larger genomes can suppress smaller ones and that suppression can occur between two suppressives. Of 48 isolates of strains carrying the suppressive viruses, 5 had newly detectable RNA species, all larger than the original suppressive genomes. At least seven genes necessary for maintenance of the wild-type killer virus (MAK genes) were needed by a suppressive mutant. No effect of ski mutations (affecting regulation of killer virus double-stranded RNA replication) on suppressiveness was observed.

Role of lysine in the replication of reovirus: I. Synthesis of complete and empty virions

Lysine is essential for the replication of infectious reovirus. Omission of lysine from the extracellular medium not only permitted the continued synthesis of structural viral proteins and viral double-stranded ribonucleic acid (RNA), but also caused an enhanced formation of viral structures which were separable by isopycnic sedimentation of CsCl into a top band consisting of empty particles with a buoyant density of 1.29 g/cm(3) and essentially free of viral RNA, and two lower bands which were difficult to resolve and had an average buoyant density of 1.37 g/cm(3). The lower bands contained most of the viral nucleic acid. The above effects were reversed when lysine was restored early after infection. In contrast, a single band with a buoyant density of 1.38 g/cm(3) was obtained from lysine-plus infected cells.

Characterization of a Ribonucleic Acid Polymerase Activity Associated with Purified Cytoplasmic Polyhedrosis Virus of the Silkworm Bombyx mori

Purified cytoplasmic-polyhedrosis virus has been found to have associated with it a polymerase activity capable of catalyzing the synthesis of virus-specific, single-stranded ribonucleic acid (RNA) from the double-stranded RNA genome.

Comparative sequence analyses of a new mammalian reovirus genome and the mammalian reovirus S1 genes from six new serotype 2 human isolates

We previously described isolation of a potentially new mammalian reovirus, designated BYD1, which can cause clinical symptoms similar to that of severe acute respiratory syndrome (SARS) in guinea pigs and macaques, from throat swabs of one SARS patient of Beijing, in 2003. For this study, we determined the genome sequences of BYD1 and the S1 gene sequences of other five mammalian reovirus isolates (BLD, JP, and BYL were isolated from different SARS patients during the outbreak, 302I and 302II were isolated from fecal specimens of two children of Beijing in 1982) to allow molecular comparison with other previously reported mammalian reoviruses (MRVs). Comparative analyses of the BYD1 genome with those of three prototype mammalian reovirus strains demonstrated that BYD1 is a novel reassortant virus, with its S1 gene segment coming from a previously unidentified serotype 2 isolate and other nine segments coming from ancestors of homologous T1L and T3D segments, which supports the hypothesis that mammalian reovirus gene segments reassort in nature. Further analyses of the S1 segments of the six isolates showed that all the isolates are novel serotype 2 MRVs based on their S1 gene sequences, which are markedly different from those of all previously reported, and the S1 genes of the four new isolates share more than 99% identity with each other, proving that they diverged from a common ancestor most recently, and the S1 genes of the four new isolates share about 65% identity with those of the two strains isolated in 1982.

Gene mapping of cytoplasmic polyhedrosis virus of silkworm by the full-length mRNA prepared under optimized conditions of transcription in vitro

Viral mRNA synthesis by the RNA polymerase associated with purified cytoplasmic polyhedrosis virus (CPV) was studied. The formation of full-length mRNA products was facilitated by including in the reaction mixture 100 mM sodium acetate, high concentrations of ribonucleoside triphosphates, and proteinase K. The 10 different species of CPV mRNAS were resolved into 9 discrete RNA bands by agarose gel electrophoresis at pH 3.5 in buffer containing 7 M urea. Each purified viral mRNA hybridized specifically to one of the viral genome segments which were separated by polyacrylamide gel electrophoresis into the 10 species of dsRNA. The relationship between the genome segments and their cognate mRNAs synthesized in vitro is thus established. Under optimal conditions of mRNA synthesis each of the genome segments was transcribed at a similar rate as determined from the yield of individual separated mRNA species. A recycling model of genome-associated RNA polymerase for viral transcription is discussed.

Relation of the structure of cytoplasmic polyhedrosis virus and the synthesis of its messenger RNA

Cytoplasmic polyhedrosis virus (CPV) was observed under an electron microscope using a combination of staining and shadowing methods. Projections, not only in positions horizontal to the grid but also vertical, were clearly visualized. When the particle was mildly disrupted with EDTA, genome dsRNA was released from a projection. If the particle was previously fixed with glutaraldehyde and then disrupted, dsRNA was released with a protein particle, which seemed to correspond to the base part of the projection. The protein particle was in most cases at the end of the strand, which sometimes takes a supercoiled structure. When CPV was incubated during mRNA synthesis, the protein particles appeared in various positions along the strands, and loop formations of dsRNA appeared. From these observations, we suggest that transcription in this virus particle proceeds as follows: genome dsRNA is transcribed by passing through the base part of the projection, where the enzymes for mRNA synthesis are located. A completed mRNA is released from the virion at the projection.

Specific binding of Bluetongue virus NS2 to different viral plus-strand RNAs

The Reoviridae have double-stranded RNA genomes of 10-12 segments, each in a single copy in the mature virion. The basis of genome segment sorting during virus assembly that ensures each virus particle contains the complete viral genome is unresolved. Bluetongue virus (BTV) NS2 is a single-stranded RNA-binding protein that forms inclusion bodies in infected cells. Here, we demonstrate that the specific interaction between NS2 and a stem-loop structure present in BTV S10 RNA, and phylogenetically conserved in other BTV serotypes, is abolished by mutations predicted to disrupt the structure. Subsequently, we mapped RNA regions in three other genomic segments of BTV that are bound preferentially by NS2. However, structure probing of these RNAs did not reveal secondary structure motifs that obviously resembled the stem-loop implicated in the NS2-S10 interaction. In addition, the specific binding by NS2 to two different viral RNAs was found to occur independently. Together, these data support the hypothesis that the recognition by NS2 of different RNA structures may be the basis for discrimination between viral RNAs during virus assembly.

The 3' sequences required for incorporation of an engineered ssRNA into the Reovirus genome

BACKGROUND

Understanding how an organism replicates and assembles a multi-segmented genome with fidelity previously measured at 100% presents a model system for exploring questions involving genome assortment and RNA/protein interactions in general. The virus family Reoviridae, containing nine genera and more than 200 members, are unique in that they possess a segmented double-stranded (ds) RNA genome. Using reovirus as a model member of this family, we have developed the only functional reverse genetics system for a member of this family with ten or more genome segments. Using this system, we have previously identified the flanking 5' sequences required by an engineered s2 ssRNA for efficient incorporation into the genome of reovirus. The minimum 5' sequence retains 96 nucleotides and contains a predicted sequence/structure element. Within these 96 nucleotides, we have identified three nucleotides A-U-U at positions 79-81 that are essential for the incorporation of in vitro generated ssRNAs into new reovirus progeny viral particles. The work presented here builds on these findings and presents the results of an analysis of the required 3' flanking sequences of the s2 ssRNA.

RESULTS

The minimum 3' sequence we localized retains 98 nucleotides of the wild type s2 ssRNA. These sequences do not interact with the 5' sequences and modifications of the 5' sequences does not result in a change in the sequences required at the 3' end of the engineered s2 ssRNA. Within the 3' sequence we discovered three regions that when mutated prevent the ssRNA from being replicated to dsRNA and subsequently incorporated into progeny virions. Using a series of substitutions we were able to obtain additional information about the sequences in these regions. We demonstrate that the individual nucleotides from, 98 to 84, 68 to 59, and 28 to 1, are required in addition to the total length of 98 nucleotides to direct an engineered reovirus ssRNA to be replicated to dsRNA and incorporated into a progeny virion. Extensive analysis using a number of RNA structure-predication software programs revealed three possible structures predicted to occur in all 10 reovirus ssRNAs but not predicted to contain conserved individual nucleotides that we could probe further by using individual nucleotide substitutions. The presence of a conserved structure would permit all ten ssRNAs to be identified and selected as a set, while unique nucleotides within the structure would direct the set to contain 10 unique members.

CONCLUSION

This study completes the characterization and mapping of the 5' and 3' sequences required for an engineered reovirus s2 ssRNA to be incorporated into an infectious progeny virus and establishes a firm foundation for additional investigations into the assortment and encapsidation mechanism of all 10 ssRNAs into the dsRNA genome of reovirus. As researchers build on this work and apply this system to additional reovirus genes and additional dsRNA viruses, a complete model for genome assortment and replication for these viruses will emerge.

Identification of the 5' sequences required for incorporation of an engineered ssRNA into the Reovirus genome

Using a reovirus reverse genetics system, we have identified the 5' sequences required of an engineered s2 ssRNA for efficient incorporation into the dsRNA genome of Reovirus. Employing an engineered, functionally active reovirus S2/CAT gene retaining the first 198 5' terminal nucleotides and the last 284 3' terminal nucleotides of the wild-type S2 segment, we have determined the 5' sequence required by a ssRNA to be recognized, replicated to dsRNA, and stably incorporated into an infectious reovirus. The 5' sequence retains 96 nucleotides of the wild-type s2 ssRNA and a predicted sequence-structure element. Within these 96 nucleotides, we have identified three nucleotides A-U-U at positions 79-81 that are essential for the incorporation of in vitro-generated ssRNAs into new reovirus progeny viral particles. This study establishes a firm foundation for additional investigation into the assortment and encapsidation mechanism of all 10 ssRNAs into the dsRNA genome of reovirus.

Reovirus type 1 associated with meningitis

A previously healthy 3-month-old girl presented with symptoms of meningitis, diarrhoea, vomiting and fever. Green monkey kidney (GMK) cells inoculated with cerebrospinal fluid (CSF) revealed reovirus-like particles by electron microscopy. RNA-gel electrophoresis, immunofluorescence and virus neutralization identified the pathogen isolated from CSF as reovirus type 1. Antibody determination by immunofluorescence of paired sera showed a significant antibody titre rise to the CSF isolate and neutralization test revealed a greater than 4-fold antibody titre rise to the CSF isolate. The CSF isolate was also neutralized by reovirus type 1 antibodies. This report represents one of a few associating reovirus with CNS symptoms in humans.

Atomic force microscopy of reovirus dsRNA: a routine technique for length measurements

Atomic force microscopy (AFM) was used to image reovirus double stranded RNA (dsRNA) deposited from diluted buffer solution onto a chemically treated mica surface. This procedure allows AFM images of dsRNA molecules to be obtained with a quality close to that obtained with conventional electron microscopy. The length of the molecules were measured directly on a computer display using the digitally acquired images. The lengths of the molecules varied between 0.2 and 1.8 microns. Statistical analysis showed a multimodal distribution with clear maxima at 0.4, 0.65 and 1.05 microns. These data are in a good agreement with those obtained by electron microscopy and gel electrophoresis.

Translational effects and sequence comparisons of the three serotypes of the reovirus S4 gene

Reovirus S4 RNA codes for the dsRNA-binding polypeptide sigma 3, a major virion outer capsid component that also has translational effects in both infected and transfected mammalian cells. To compare the composition and properties of the three different serotypes of sigma 3, a DNA copy of the type 2 gene was cloned and sequenced. The total lengths (1196) and the sequences of leader (33 nucleotides) and trailer (66 nucleotides) regions are highly conserved among the three S4 serotypes. The type 1 and 3 S4 genes are highly related (77 mismatches). However, the type 2 gene contains many mismatches relative to the type 1 and 3 genes (260 and 270 positions, respectively). Most of the mismatches are third position changes, resulting in sigma 3 polypeptides that are 90% or more identical. Transient expression vectors, constructed by replacing the chloramphenicol acetyltransferase (CAT) gene in pRSVCAT with S4 DNA, were used to test the effects of polypeptide sigma 3 on CAT expression in cotransfected COS cells. Transfection with the correctly oriented DNAs resulted in synthesis of the corresponding sigma 3 polypeptides which enhanced CAT expression. The type 2 and type 3 S4 genes were considerably more stimulatory than type 1 when compared to CAT DNA alone. However, with all three serotypes the CAT activity was significantly higher in cells cotransfected with S4 DNA in the correct orientation as compared to the reverse arrangement.

Functional expression and RNA binding analysis of the interferon-induced, double-stranded RNA-activated, 68,000-Mr protein kinase in a cell-free system

Eukaryotic viruses have devised numerous strategies to downregulate activity of the interferon-induced, double-stranded (dsRNA)-activated protein kinase (referred to as p68 on the basis of its Mr of 68,000 in human cells). Viruses must exert this control to avoid extensive phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF-2) by p68 and the resultant negative effects on protein synthesis initiation. To begin to define the molecular mechanisms underlying this regulation, we optimized expression of p68 in an in vitro transcription-translation system utilizing the full-length cDNA clone. The in vitro-expressed kinase was autophosphorylated in response to dsRNAs and heparin in a manner similar to that for the native p68 provided that the kinase inhibitor, 2-aminopurine, was present during the in vitro translation reaction. Further, the activated kinase efficiently phosphorylated its natural substrate, the alpha subunit of eIF-2. Binding experiments revealed that the expressed kinase complexed with the dsRNA activator, reovirus dsRNA, as well as the adenovirus-encoded inhibitor, VAI RNA. Interestingly, both the reovirus RNAs and VAI RNA also complexed with protein kinase molecules that lacked the carboxyl terminus and all catalytic domains. Deletion analysis confirmed that the p68 amino terminus contained critical determinants for reovirus dsRNA and VAI RNA binding. Further, reovirus dsRNA efficiently bound to, but failed to activate, p68 kinase molecules containing a single amino acid substitution in the invariant lysine 295 present in catalytic domain II. Taken together, these data demonstrate that this expression system permits a detailed mutagenic analysis of the regions of p68 required for interaction with virus-encoded activators and repressors.

Functional expression and RNA binding analysis of the interferon-induced, double-stranded RNA-activated, 68,000-Mr protein kinase in a cell-free system

Eukaryotic viruses have devised numerous strategies to downregulate activity of the interferon-induced, double-stranded (dsRNA)-activated protein kinase (referred to as p68 on the basis of its Mr of 68,000 in human cells). Viruses must exert this control to avoid extensive phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF-2) by p68 and the resultant negative effects on protein synthesis initiation. To begin to define the molecular mechanisms underlying this regulation, we optimized expression of p68 in an in vitro transcription-translation system utilizing the full-length cDNA clone. The in vitro-expressed kinase was autophosphorylated in response to dsRNAs and heparin in a manner similar to that for the native p68 provided that the kinase inhibitor, 2-aminopurine, was present during the in vitro translation reaction. Further, the activated kinase efficiently phosphorylated its natural substrate, the alpha subunit of eIF-2. Binding experiments revealed that the expressed kinase complexed with the dsRNA activator, reovirus dsRNA, as well as the adenovirus-encoded inhibitor, VAI RNA. Interestingly, both the reovirus RNAs and VAI RNA also complexed with protein kinase molecules that lacked the carboxyl terminus and all catalytic domains. Deletion analysis confirmed that the p68 amino terminus contained critical determinants for reovirus dsRNA and VAI RNA binding. Further, reovirus dsRNA efficiently bound to, but failed to activate, p68 kinase molecules containing a single amino acid substitution in the invariant lysine 295 present in catalytic domain II. Taken together, these data demonstrate that this expression system permits a detailed mutagenic analysis of the regions of p68 required for interaction with virus-encoded activators and repressors.

Functional expression and characterization of the interferon-induced double-stranded RNA activated P68 protein kinase from Escherichia coli

The P68 protein (referred to as P68 on the basis of its molecular weight of 68,000 in human cells) is a serine/threonine kinase induced by interferon treatment and activated by double-stranded (ds) RNAs. Although extensively studied, little is currently known about the regulation of kinase function at the molecular level. What is known is that activation of this enzyme triggers a series of events which lead to an inhibition of protein synthesis initiation and may, in turn, play an integral role in the antiviral response to interferon. To begin to understand P68 and its biological functions in the eukaryotic cell, we have expressed the protein kinase in Escherichia coli under control of the bacteriophage T7 promoter. In rifampicin-treated cells, metabolically labeled with [35S]methionine and induced by IPTG, the P68 kinase was the predominant labeled product. Further, P68 was recovered from extracts as a fully functional enzyme, shown by its ability to become activated and phosphorylate its natural substrate, the alpha subunit of eukaryotic protein synthesis initiation factor 2 (eIF-2). Moreover, P68 was phosphorylated in vivo in E. coli, providing conclusive evidence that the kinase has the capacity to phosphorylate and activate itself in the absence of other eukaryotic proteins. In contrast, a mutant P68 protein, containing a single amino acid substitution in the invariant lysine in catalytic domain II, was completely inactive. Interestingly, both the mutant and wild-type protein kinases efficiently bound activator dsRNAs despite the fact that only the latter was activated by these RNAs. Finally, the expressed kinase could be isolated from contaminating E. coli proteins in an active form by immunoaffinity chromatography with a monoclonal antibody specific for P68.

Structure-specific binding of wound tumor virus transcripts by a host factor: involvement of both terminal nucleotide domains

A gel retardation assay was used to demonstrate binding of wound tumor virus transcripts by a protein component of leafhopper vector cell extracts. Comparative binding studies employing terminally modified and internally deleted transcripts established that the segment-specific inverted repeats present in the terminal domains of the viral transcripts were necessary but not sufficient for optimal binding. An additional involvement of internal sequences in either the formation or the stabilization of the binding complex was indicated. Results of competitive binding experiments confirmed the sequence- and structure-specificity of the protein-RNA interaction and revealed apparent differences in the ability of individual viral transcripts to form a stable binding complex. Possible implications of structure-specific interactions between wound tumor virus transcripts and a host component and the role of the terminal inverted repeats are discussed.

Characteristics and analysis of electropherotypes of avian reovirus field isolates

Genomic segments of 10 selected isolates of avian reoviruses recovered from the intestine of birds affected with malabsorption syndrome or runting/stunting syndrome were separated by polyacrylamide gel electrophoresis. Different electropherotypes were observed and analysed, depending on the period of recovery and particular geographic locations. The analysis showed great variability in the dsRNA profiles of the isolates and higher mobility of the segments L1, S1, S2, S3 and S4. There was no correlation between electropherotype and geographic origin of the isolate. The analysis also showed the emergence of electropherotypically distinct strains since the introduction of modified live reovirus vaccines.

Characterization of a common high-affinity receptor for reovirus serotypes 1 and 3 on endothelial cells

During viremia, viruses may be cleared from the bloodstream and taken up by specific organs. The uptake of virus from the bloodstream is dependent on the association of viral particles with endothelial cells that line the luminal surfaces of large and small blood vessels. To understand the nature of this interaction, we have studied the binding of reovirus serotypes 1 and 3 to these cells in vitro. Both serotypes of reovirus productively infected endothelial cells. By using [35S]methionine-biolabeled reovirus as a tracer ligand, we found that both viruses rapidly bind to endothelial cells and that equilibrium is reached after 4 h. The binding of the radiolabeled viruses was saturable and mediated by a homogeneous population of cellular receptors with very high affinity (Kd = 0.5 nM) for the virus ligands. Both serotypes bind to the same receptor, since the attachment of each radiolabeled serotype is inhibited by both the homologous and heterologous unlabeled virus. Exposure of labeled virus to monoclonal antibodies directed against the viral hemagglutinin (sigma 1 protein) inhibited binding, demonstrating that the attachment of reovirus to endothelial cells is mediated by the hemagglutinin for both serotypes. By using a novel ligand-blotting assay, the binding of both viruses to a 54,000-dalton protein could be demonstrated. The binding of each radiolabeled serotype to this protein was inhibited by the homologous and heterologous unlabeled serotype. By using cell fractionation after homogenization, we demonstrated that this 54-kilodalton protein is a membrane protein, in agreement with its proposed role as a cell surface receptor for reovirus serotypes 1 and 3.

Accuracy of rotavirus diagnosis: modified genome electrophoresis versus electron microscopy

530 human faecal samples were examined for the presence of rotavirus by electron microscopy (EM) and by a modified electrophoretic analysis of viral genome (PAGE). 516 stools gave identical results by both methods (97.4% agreement). The proportion of EM+, PAGE- samples (1/530) was significantly lower than the proportion of EM-, PAGE + samples (13/530) (P less than 0.01 with McNemar test). Relative sensitivity was 99.6% for PAGE and 95% for EM. False positive results could be excluded for each method because of the characteristic morphology of rotavirus particles (EM) and specificity of rotavirus electrophoretypes (PAGE). Discrepant cases were reexamined whenever possible and the causes of misdiagnosis are discussed.

Molecular cloning and sequencing of the gene (M2) encoding the major virion structural protein (mu 1-mu 1C) of serotypes 1 and 3 of mammalian reovirus

Full-length c-DNA copies of the M2 gene from the Lang strain of type 1 and the Dearing strain of type 3 reovirus have been cloned in the Escherichia coli plasmid pAT153. DNA sequencing of these clones showed that the type 3 gene was 2207 nucleotides long and the single long open reading frame encoded a primary translation product (mu 1) of 709 amino acids with a molecular weight of 76,000. The type 1 gene was three nucleotides shorter at 2204 with the deletions occurring near the center of the coding sequence so that the primary translation product of this gene was one amino acid shorter at 708. Sequence homology between the two genes had an overall value of 85%, rising to 95% when only the noncoding sequences were compared. The 334 nucleotide changes between the two genes were distributed throughout the sequence with no apparent areas of concentration. Comparison of the predicted amino acid sequences showed that there were 24 differences between the two giving a homology of 96.6% at the protein level. The amino acid changes of which only 9 were nonconservative were again spread fairly evenly throughout the coding sequence although there was one small patch of 5 changes in a stretch of 10 amino acids near the carboxyl terminus. The post-translational cleavage to convert mu 1 to the major virion protein mu 1C is revealed as involving the removal of 42 amino acids exclusively from the amino terminus of mu 1. Simple addition of trypsin-sensitive cleavage sites or predicted secondary structure failed to show the cause of the large difference known to exist in the protease sensitivities of virions carrying these two proteins.

Reovirus major capsid protein expressed in Escherichia coli

A DNA copy of the open reading frame of the S4 gene of reovirus type 3 was cloned into a temperature-regulated bacterial expression vector. Induction at 42 degrees C resulted in the synthesis of a polypeptide that comigrated with virion capsid protein sigma 3 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and reacted with sigma 3-specific antisera. The protein was expressed in bacteria as insoluble aggregates that accumulated in polar inclusion bodies. Aggregated product also resulted when the expression system was manipulated to induce bacterial sigma 3 (b sigma 3) synthesis at temperatures below 42 degrees C. Various methods used to solubilize b sigma 3 did not yield the monomeric protein. The results indicate that sigma 3, the major surface component of reovirions, is expressed in transfected Escherichia coli as an aggregated, disulfide cross-linked protein.

Synthesis in Escherichia coli of the reovirus nonstructural protein sigma NS

The coding region of reovirus type 3 genomic segment S3, encoding the nonstructural protein sigma NS, was placed under the control of the bacteriophage lambda pL promoter in the Escherichia coli expression plasmid pRC23 (J.C. Lacal, E. Santos, V. Notario, M. Barbacid, S. Yamazaki, H.-F. Kung, C. Seamans, S. McAndrew, and R. Crowl, Proc. Natl. Acad. Sci. USA 81:5305-5309). Derepression of the pL promoter led to the synthesis of a protein of the same molecular weight as sigma NS produced in reovirus-infected L cells. The expressed protein was indistinguishable from authentic sigma NS by peptide mapping with Staphylococcus aureus V8 protease and by immunoblot analysis. Most importantly, the purified protein had nucleic acid-binding properties similar to that previously shown for sigma NS obtained from infected cells. Binding of single-stranded RNAs by recombinant sigma NS protein was inhibited by GTP.

The characterization and molecular cloning of the double-stranded RNA genome of an Australian strain of infectious bursal disease virus

The genome of infectious bursal disease virus (IBDV) strain 002-73 was found to consist of two segments of double-stranded (ds) RNA which were 3400 bp (MW 2.06 X 10(6)) and 2900 bp (MW 1.76 X 10(6)) long, respectively. The ds IBDV RNA could be translated, in vitro, only after extensive denaturation. The small RNA segment was found to code for a single polypeptide of MW 90K, while the large RNA segment coded for three major polypeptides of MW 52K, 32K, and 28K, and two minor polypeptides of MW 41K and 16K. The large RNA segment could encode proteins of MW 125K while the MW of the translated products was 169K suggesting that a precursor-product relationship exists between some of the translation products. A method is described for the synthesis of ds cDNA from large ds RNA molecules. Analyses of recombinant colonies showed that inserts covering the entire IBDV genome had been cloned.