Sequence analysis of the gene (6) encoding the major capsid protein (VP6) of group C rotavirus: higher than expected homology to the corresponding protein from group A virus

A milk-based self-assemble rotavirus VP6-ferritin nanoparticle vaccine elicited protection against the viral infection

BACKGROUND

Rotavirus is the leading cause of severe dehydrating diarrhea in young children and the inner capsid protein VP6 is a potential vaccine candidate that can induce cross-protective immune responses against different Rotavirus strains. The use of ferritin nanoparticles as the scaffold of the antigen can improve the immunogenicity of the subunit vaccines and provide broader protection. We here present a non-live and self-assemble recombinant rotavirus VP6-ferritin (rVP6-ferritin) nanoparticle vaccine.

RESULTS

The rVP6-ferritin nanoparticles were expressed in E. coli and self-assembled to uniform spherical structure which similar to ferritin, and oral administration of them induced efficient humoral and mucosal immunogenicity in mice. The nanoparticles were further transgenically expressed in the milk of mice, and pup mice breastfed by transgenic rVP6-ferritin mothers had strongly induced immunogenicity and-compared to pups breastfed by wild type mothers-the proportion of rotavirus challenged pups with diarrhea symptoms, the duration and intensity of the diarrhea, and the deleterious effects on overall growth resulting from the diarrhea were all significantly reduced.

CONCLUSIONS

These results suggest that this recombinant VP6-ferritin nanoparticle vaccine can efficiently prevent the death and malnutrition induced by the rotavirus infection in infants and is a promising candidate vaccine for rotavirus.

Diarrhea caused by rotavirus A, B, and C in suckling piglets from southern Brazil: molecular detection and histologic and immunohistochemical characterization

Rotavirus (RV) is an important viral pathogen causing diarrhea in piglets and other mammals worldwide. We describe 34 cases from 4 diarrheal outbreaks caused by RV in unvaccinated farrowing units in southern Brazil from 2011 to 2013. We performed autopsy, histologic examinations, bacterial culture, RV immunohistochemistry (IHC), and enteric virus detection through molecular assays for rotavirus A, B, and C, transmissible gastroenteritis virus, porcine epidemic diarrhea virus, sapovirus, norovirus, and kobuvirus. Histologically, villus atrophy (29 of 34) and epithelial vacuolation (27 of 34) occurred in all 4 outbreaks. Cell debris in the lamina propria occurred in 20 cases, mostly from outbreaks A (8 of 11), C (4 of 6), and D (7 of 11). IHC was positive for RV in 21 of 34 samples. RT-PCR was positive for RV in 20 of 30 samples; RV-C was the most frequently detected RV ( n = 17). Kobuvirus was detected in 11 samples, and, in 3 of them, there was single detection of this enteric virus.

Rotavirus NSP1 Requires Casein Kinase II-Mediated Phosphorylation for Hijacking of Cullin-RING Ligases

The rotavirus nonstructural protein NSP1 repurposes cullin-RING E3 ubiquitin ligases (CRLs) to antagonize innate immune responses. By functioning as substrate adaptors of hijacked CRLs, NSP1 causes ubiquitination and proteasomal degradation of host proteins that are essential for expression of interferon (IFN) and IFN-stimulated gene products. The target of most human and porcine rotaviruses is the β-transducin repeat-containing protein (β-TrCP), a regulator of NF-κB activation. β-TrCP recognizes a phosphorylated degron (DSGΦXS) present in the inhibitor of NF-κB (IκB); phosphorylation of the IκB degron is mediated by IκB kinase (IKK). Because NSP1 contains a C-terminal IκB-like degron (ILD; DSGXS) that recruits β-TrCP, we investigated whether the NSP1 ILD is similarly activated by phosphorylation and whether this modification is required to trigger the incorporation of NSP1 into CRLs. Based on mutagenesis and phosphatase treatment studies, we found that both serine residues of the NSP1 ILD are phosphorylated, a pattern mimicking phosphorylation of IκB. A three-pronged approach using small-molecule inhibitors, small interfering RNAs, and mutagenesis demonstrated that NSP1 phosphorylation is mediated by the constitutively active casein kinase II (CKII), rather than IKK. In coimmunoprecipitation assays, we found that this modification was essential for NSP1 recruitment of β-TrCP and induced changes involving the NSP1 N-terminal RING motif that allowed formation of Cul3-NSP1 complexes. Taken together, our results indicate a highly regulated stepwise process in the formation of NSP1-Cul3 CRLs that is initiated by CKII phosphorylation of NSP1, followed by NSP1 recruitment of β-TrCP and ending with incorporation of the NSP1–β-TrCP complex into the CRL via interactions dependent on the highly conserved NSP1 RING motif.

Rotavirus is a segmented double-stranded RNA virus that causes severe diarrhea in young children. A primary mechanism used by the virus to inhibit host innate immune responses is to hijack cellular cullin-RING E3 ubiquitin ligases (CRLs) and redirect their targeting activity to the degradation of cellular proteins crucial for interferon expression. This task is accomplished through the rotavirus nonstructural protein NSP1, which incorporates itself into a CRL and serves as a substrate recognition subunit. The substrate recognized by the NSP1 of many human and porcine rotaviruses is β-TrCP, a protein that regulates the transcription factor NF-κB. In this study, we show that formation of NSP1 CRLs is a highly regulated stepwise process initiated by CKII phosphorylation of the β-TrCP recognition motif in NSP1. This modification triggers recruitment of the β-TrCP substrate and induces subsequent changes in a highly conserved NSP1 RING domain that allow anchoring of the NSP1–β-TrCP complex to a cullin scaffold.

Detection and quantitation of group A rotaviruses by competitive and real-time reverse transcription-polymerase chain reaction

A competitive reverse transcription-polymerase chain reaction (RT-PCR) was developed to detect and to quantitate the RNA of group A rotaviruses. In the assay, a 433 bp fragment is amplified by a one-tube RT-PCR protocol using primers with binding sites located in a highly conserved region of segment 6 of the rotavirus genome. An in vitro synthesized RNA with a 43-base deletion with respect to the wild-type sequence of this fragment was used as an internal control. Using these transcripts as templates, 10 RNA molecules were amplified reproducibly and detected in ethidium bromide-stained agarose gels or by fluorimetry using the SYBR Green I dye in a real-time RT-PCR assay. The efficiency of the protocol was confirmed by the detection of small amounts of viral RNA of group A rotaviruses in clinical samples obtained from various animal species and man.

Production of hybrid double- or triple-layered virus-like particles of group A and C rotaviruses using a baculovirus expression system

Dual infections by group A and group C rotaviruses have been reported, but no reassortants between group A and group C rotaviruses have been described. The VP6 major inner capsid protein of group A and C rotaviruses shares common antigens detected by monoclonal antibodies and also shares 40-43% amino acid identity. Coinfection of Spodoptera frugiperda (Sf9) insect cells with different combinations of the recombinant baculoviruses encoding either group A [RF VP2 (A-VP2), IND VP6 (A-VP6), and VP7 (A-VP7[IND]), 2292B VP7 (A-VP7[2292B])] or C [Shintoku VP6 (C-VP6) and VP7 (C-VP7)] bovine rotavirus proteins produced hybrid group A/C triple-layered VP2/6/7 virus-like particles (TLPs) composed of A-VP2/C-VP6/C-VP7, A-VP2/C-VP6/A-VP7(IND), A-VP2/C-VP6/A-VP7(2292B), and A-VP2/A-VP6/C-VP7. To our knowledge, this is the first report that the inner capsid VP6 of group A or group C rotavirus can support attachment of the heterologous, antigenically distinct group A (G6, IND or G10, 2292B) or group C rotavirus outer capsid VP7 to produce hybrid TLPs in vitro.

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.

Lack of evidence for rotavirus by polymerase chain reaction/enzyme immunoassay of hepatobiliary samples from children with biliary atresia

The purpose of this study was to analyze hepatobiliary samples of patients with biliary atresia for rotavirus groups. A, B, and C, because group A rotavirus had been used to produce an animal model of the disease and group C rotavirus had been found in hepatobiliary samples from one group of patients. Biliary remnants and liver tissue from 10 biliary atresia and 14 control patients with other liver diseases were examined for rotavirus groups A, B, and C using nonisotopic, reverse transcriptase polymerase chain reaction enzyme immunoassay. Biliary atresia patients had a median age of 3 mo and were from a confined geographic area. Rotaviral stocks from groups A and C were used as polymerase chain reaction-positive controls. The limits of detection for rotaviral RNA from these two groups were respectively, 5 plaque-forming units and 50 tissue culture infectious doses (ID50). Tissue culture was 100-fold less sensitive for groups A and C than the polymerase chain reaction. The nested nonisotopic probes hybridized in solution only with their homologous target DNAs as determined by the enzyme immunoassay, or by Southern blot hybridization. Although it was possible to detect mRNA from a beta-actin housekeeping gene in all of the hepatobiliary samples, no evidence of rotaviral RNA was found in either the biliary atresia or the negative control group. In conclusion, rotavirus is not a common viral etiology of biliary atresia.

An occurrence of diarrheal cases associated with group C rotavirus in adults

Six of the 23 college students who joined a group trip in February of 1991 developed acute nonbacterial gastroenteritis with severe diarrhea. The causal agent was identified as group C rotaviruses by electron microscopy (EM), immune-EM (IEM) and the molecular examinations including polyacrylamide gel electrophoresis (PAGE) and polymerase chain reaction (PCR) on virus particles detected in the extract of watery fecal specimens of the patients. The patients positive for virus isolation showed significant increase in IEM antibody to the isolated virus in their paired sera. These findings suggest that the group C rotavirus is an important etiological agent of diarrhea and may also cause serious food-borne diarrheal disease in adults.

Sequence analysis of three non structural proteins of a porcine group C (Cowden strain) rotavirus

Sequences of three gene products of a group C (Cowden strain) rotavirus are presented and compared with the sequences of the corresponding group A (SA11) proteins. The degree of similarity for gene 7, 9, and 10 is respectively 34%, 58%, and 45%. Comparison of these 2 viruses allowed to identify several regions well conserved. In the protein coded by Cowden segment 7 (NS 53) only a short cystein and histidine rich region, presenting the zinc finger consensus motif, is common to group A (segment 5) and group C sequences. Conversely the protein coded by segment 9 (NS 35) presented marked homology with group A NS 35. The protein coded by segment 10 (NS 26) is serine rich and presents an accumulation of charged residues near the carboxy terminus, like group A counterpart. This genomic segment presented a single large open reading frame, that contrasts with the group A counterpart for which a second out of phase ORF is used in rotavirus infected MA 104 cells.

Production and characterization of monoclonal antibodies to porcine group C rotaviruses cross-reactive with group A rotaviruses

Five monoclonal antibodies (MAbs) to porcine group (gp) C rotaviruses (Cowden and Ah strains) reactive with both gp A and C rotaviruses in cell culture immunofluorescence (CCIF) tests were produced and characterized. These MAbs reacted with three strains of gp A and two strains of gp C rotaviruses in a CCIF test and were classified into two groups based on their CCIF titers. The MAbs also reacted to various degrees with cell-culture-propagated porcine gp C rotavirus (Cowden) and bovine gp A rotavirus (NCDV) in an enzyme-linked immunosorbent assay by using the MAbs as capture antibodies. Fecal samples containing human, bovine, and porcine strains of gp A and C rotaviruses were positive when tested using one of the MAbs in this assay. The MAbs recognized VP6 of gp A rotavirus and the VP6 counterpart (41-kDa protein) of gp C rotavirus in a Western blot assay. Results of competitive binding assays on four MAbs indicated that gp A and gp C rotaviruses share three overlapping epitopes within a single antigenic domain. These results suggest that gp A and C rotaviruses share a common antigen located on the VP6 protein, which is recognized by certain MAbs in various serologic assays.

Expression of the major capsid protein VP6 of group C rotavirus and synthesis of chimeric single-shelled particles by using recombinant baculoviruses

VP6 of group C (Cowden strain) rotavirus was expressed in the baculovirus system. The recombinant protein, expressed to a high level in insect cells, was purified by ion-exchange chromatography. The purified protein was proven to be trimeric. The effect of pH on the trimer's stability was investigated. Coexpression of VP6 from group A (bovine strain RF) and VP6 from group C in the baculovirus system did not result in the formation of chimeric trimers. Coexpression of VP2 from group A rotavirus (bovine strain RF) and VP6 from group C in the baculovirus system led to the formation of chimeric, empty, single-shelled particles. These results demonstrate conservation in the domains necessary for binding to VP2 in different serogroups of VP6. The locations of the domains involved in trimerization and in the interaction with VP2 are discussed.

The correct sequence of the porcine group C/Cowden rotavirus major inner capsid protein shows close homology with human isolates from Brazil and the U.K

Amino acid sequence alignments between the human group C/Bristol and the published porcine group C/Cowden VP6 proteins have revealed a region of extreme sequence divergence. We have been unable to confirm the nucleotide sequence of the Cowden VP6 gene corresponding to this region of divergence. Direct sequencing of a PCR-amplified cDNA pool has revealed a frame shift, and three nucleotide changes, within the published sequence of the porcine (Cowden) VP6 gene. The corrected sequence of the porcine protein revealed a closer homology with VP6 from the Bristol strain and two new human group C rotavirus isolates. Atypical rotaviruses have been detected in the feces of children living in Belém, Brazil, and Preston, U.K. Direct sequencing of PCR-amplified cDNA corresponding to the VP6 gene of one isolate from each location confirmed the presence of a group C rotavirus. The complete nucleotide sequences of the VP6 genes from the group C/Belém and C/Preston rotaviruses contained an open reading frame of 1185 nucleotides (395 amino acids; deduced M(r) 44,669 Da). The Belém VP6 gene demonstrated 97.9% nucleotide homology with the human group C/Bristol VP6 gene and 83.4% nucleotide homology (91.6% deduced amino acid homology) with the corrected porcine group C/Cowden sequence. The Preston VP6 gene demonstrated 99.6% nucleotide homology with the human group C/Bristol VP6 gene and 84.0% nucleotide homology (91.6% deduced amino acid homology) with the corrected porcine group C/Cowden sequence. Remarkably, the deduced amino acid sequence of the Brazilian strain was identical to that of the U.K. isolates.

Nucleotide sequence of gene 5 encoding the inner capsid protein (VP6) of bovine group C rotavirus: comparison with corresponding genes of group C, A, and B rotaviruses

To further study the molecular characteristics of group (gp) C rotaviruses, we produced, cloned, and sequenced cDNA to gene 5 of the Shintoku strain of bovine gp C rotavirus. The resulting clone was specific for gene 5 and was genetically related to the human and porcine gp C rotaviruses, as demonstrated by Northern blot hybridization analysis. The Shintoku gene 5 is 1352 nucleotides in length and has one open reading frame encoding a polypeptide of 395 amino acids with a predicted molecular mass of 44.5 kDa. Comparative sequence analysis indicated that: (i) the Shintoku gene 5 protein shared 88.4 to 90.6% homology with the VP6 of the human (Bristol and 88-220) and porcine (Cowden) strains of gp C rotaviruses, but only low homology with the VP6 of bovine gp A (RF) and human gp B (ADRV) rotaviruses (41.3 and 16.3%, respectively); (ii) the predicted secondary structure was highly conserved among the gene 5 proteins of the bovine, porcine, and human gp C rotaviruses; and (iii) seven highly conserved regions were identified for the first time in the deduced primary amino acid sequences of gene 5 of gp C and gene 6 of gp A rotaviruses. However, only three of these highly conserved areas were present in the regions of VP6, where the secondary structure was predicted to be similar for the rotavirus strains examined. These three regions may contribute to common epitopes between the two groups of rotaviruses. Our results, in comparison with data for other rotaviruses, indicate that gene 5 of the bovine gp C rotavirus codes for the major inner capsid protein (VP6).

Development of a biotin-streptavidin-enhanced enzyme-linked immunosorbent assay which uses monoclonal antibodies for detection of group C rotaviruses

A biotin-streptavidin-enhanced enzyme-linked immunosorbent assay (ELISA) which uses monoclonal antibodies (MAbs) for the detection of group C rotaviruses was developed. An assay in which plates were coated with three pooled MAbs and biotinylated polyclonal immunoglobulin G (IgG) (polyclonal antibody [PAb]) was used as the detector (MAb capture-PAb detector) was found to be the most sensitive and specific of the assays when it was compared with assays in which plates were coated with polyclonal antiserum and detection was done with either biotinylated polyclonal antiserum (PAb capture-PAb detector) or biotinylated pooled MAbs (PAb capture-MAb detector). The MAb capture-PAb detector ELISA detected 83% of samples confirmed to be positive for group C rotaviruses, whereas the PAb capture-PAb detector assay detected 63% of positive samples and the PAb capture-MAb detector assay detected 65% of positive samples. All three procedures detected both of the bovine and the two human group C rotaviruses, but none of the three procedures detected fecal samples containing group A and B rotaviruses or fecal samples negative for group C rotaviruses used in this study. The sensitivity of the MAb capture-PAb detector ELISA was determined by serially diluting fecal group C rotaviruses; antigens were detected in maximal positive dilution ranges of 1:1,000 to 1:3,000 for the samples tested. On the basis of the cell culture immunofluorescence assay infectivity titer of semipurified cell culture-passaged Cowden group C rotavirus, the sensitivity of the MAb capture-PAb detection ELISA for detection of homologous group C rotavirus was 53 fluorescent focus units per ml. Epitope mapping by use of the biotinylated MAbs in competition assay suggested that our MAbs may bind to three different but overlapping epitopes. These results suggest that the MAb capture-PAb detector ELISA can be used to study the epidemiology of group C rotaviruses in humans and animals.

Molecular cloning, sequence analysis, in vitro expression, and immunoprecipitation of the major inner capsid protein of the IDIR strain of group B rotavirus (GBR)

The sixth genomic segment of the infectious diarrhea of infant rats (IDIR) strain of group B rotavirus (GBR) was cloned from double-stranded RNA purified from infected rat feces. Sequence comparison with group A rotaviruses (GAR) and the human ADRV strain of GBR indicated that IDIR gene 6 encoded the major inner capsid protein. The nucleic acid sequences of the two GBR genes were 72.9% conserved, and 83.4% of the amino acids were identical. Sequence substitutions between IDIR and ADRV were more numerous than reported for heterologous GAR strains, indicating that the two GBR strains may have diverged from one another over a longer period of time. Despite the sequence heterogeneity exhibited by the major inner capsid proteins of ADRV and IDIR, hydrophilicity plots of the two gene products were nearly indistinguishable. The GBR hydrophilicity plots displayed little similarity with those of rotavirus groups A or C, indicating substantial differences in the structures of those major inner capsid proteins. In vitro transcription and translation of IDIR gene 6 yielded a polypeptide product consistent in size with that predicted from the deduced amino acid sequence and the virion major inner capsid protein. The IDIR 6 polypeptide was immunoprecipitated by antisera directed against IDIR as well as antisera directed against ADRV and a heterologous bovine strain of GBR. No immunoprecipitation was observed with control sera or antisera directed against GAR. These results confirmed that group-specific epitopes were displayed by the major inner capsid protein encoded by IDIR gene 6. Reactivity with heterologous GBR antisera also indicated that the IDIR gene 6 product may prove useful as a standard reagent in immunoassays for the detection of GBR.

Analysis of the genetic diversity of genes 5 and 6 among group C rotaviruses using cDNA probes

Two partial cDNA clones of genes 5 (encoding the major inner capsid protein VP 6) and 6 (encoding a nonstructural protein) of the porcine group (Gp) C rotavirus (Cowden strain) were radiolabeled with 32P and used individually as probes in Northern and dot blot hybridization assays. The specificity of each probe was tested against genomic dsRNA from: (1) porcine Gp A, B, and C rotaviruses; (2) Gp C rotaviruses from different species; and (3) porcine Gp C rotavirus field strains with varying electropherotype patterns. Neither probe hybridized with ds RNA from the porcine Gp A and B strains under the stringency conditions employed in the study. However, the gene 5 probe hybridized with the corresponding gene from the homologous porcine and the heterologous human and bovine Gp C rotaviruses tested. The gene 6 probe hybridized with the corresponding gene from the homologous Cowden strain, but hybridized weakly with gene 6 from the human and bovine Gp C rotaviruses. Both probes recognized all six different porcine Gp C field strains, although with varying intensities. Our results demonstrate that the gene 5 and 6 probes used in this study are specific for Gp C rotaviruses. However, evidence for greater genetic variation in the gene 6 among porcine, bovine and human Gp C strains suggested that the gene 5 probe may prove more broadly reactive among Gp C strains from different species. cDNA probes used in our study should prove useful for the detection of Gp C rotaviruses in feces and facilitate epidemiologic studies.

Cloning of noncultivatable human rotavirus by single primer amplification

A novel, sequence-independent strategy has been developed for the amplification of full-length cDNA copies of the genes of double-stranded RNA (dsRNA) viruses. Using human (Bristol) group C rotavirus as an example, a single amino-linked modified oligonucleotide (primer 1) was ligated to either end of each dsRNA genome segment by using T4 RNA ligase. Following reverse transcription, annealing, and repair of cDNA strands, amplification of the viral dsRNA genome was accomplished by polymerase chain reaction using a single complementary oligonucleotide (primer 2). Northern (RNA) hybridization of cDNA to virus dsRNA indicated that it was possible to generate cDNA representing the complete genome from very small clinical samples. This technique was used to determine the complete nucleotide sequence (728 bp) and coding assignment of gene 10, which revealed an open reading frame of 212 amino acids with limited homology to NS26 from human group A rotavirus. In contrast to previous tailing methods, the addition of one defined primer allowed unequivocal identification of terminal nucleotides and should be generally applicable to viruses with segmented dsRNA genomes and especially for analysis of clinical samples, for which very limited quantities of biological material are available.

Sequences of the four larger proteins of a porcine group C rotavirus and comparison with the equivalent group A rotavirus proteins

The sequences of the four larger proteins of rotavirus group C (Cowden strain) are presented and compared with the sequences of the corresponding group A proteins. They exhibit a significant level of homology, allowing gene coding assignment for the group C rotavirus. The coding strategy of the group C virus RNA segment is the same as that for the group A large segments as one long open reading frame is present in each segment. The genome segment 1 encodes the structural protein VP1 which presents the RNA-dependent RNA polymerase consensus motifs. The VP1 protein is the most highly conserved between the rotaviruses of groups A and C. The genome segment 2 encodes the VP2 protein. The deduced protein sequence does not present the putative leucine zippers identified in the group A protein but its amino terminal is hydrophilic and highly charged as previously noted for the group A protein. The genome segment 3 encodes for a protein homologous to the group A outer capsid protein VP4. As observed among the various group A sequences, the amino terminal is the region presenting the fewest similarities. A cleavage region and a putative fusion motif similar to those present in the group A viruses have been identified. For this protein the comparison has been extended to the IDIRV [corrected] VP3 previously sequenced and indicates that groups A and C VP4 proteins are much more related to each other than to the group B equivalent. The genome segment 4 encodes for a protein showing an approximate 40% sequence identity to the minor core protein, VP3, of the group A rotavirus. This remarkable conservation of primary structures argues for severe functional constraint on the evolution of these proteins.

Isolation, characterization, and serial propagation of a bovine group C rotavirus in a monkey kidney cell line (MA104)

A virus (designated the Shintoku strain) which was morphologically indistinguishable from group A rotaviruses was detected in the feces of adult cows with diarrhea in Japan. The virus contained 11 segments of double-stranded RNA and had an electrophoretic migration pattern in polyacrylamide gels similar to that of other group C rotaviruses (4-3-2-2). Feces containing the bovine virus reacted with antiserum to porcine group C rotavirus (Cowden strain) but not group A or B rotaviruses in immunoelectron microscopy. The virus was adapted to serial propagation in roller tube cultures of a rhesus monkey kidney cell line (MA104) by using high concentrations of trypsin. Evidence for viral replication in MA104 cell cultures was demonstrated by immunoelectron microscopy and indirect immunofluorescence by using antiserum to porcine group C rotavirus and by electrophoretic analysis of extracted viral double-stranded RNA. A significant antibody response against the isolate was detected in convalescent-phase sera of cows which excreted the virus: no increased antibody response to bovine group A rotavirus was observed. To our knowledge, this is the first isolation of a group C rotavirus from cattle.

Molecular cloning, sequence analysis and coding assignment of the major inner capsid protein gene of human group C rotavirus

The VP6 gene of human group C rotavirus was cloned and sequenced. Hybridization to the human group C and the porcine group C/Cowden dsRNA genomes assigned this coding sequence to segment 5. The complete human VP6 sequence contained an open reading frame of 1185 nucleotides (395 amino acids; deduced Mr 44,669 Da). The protein sequence demonstrated low homology with the group A VP6 sequences (41.7 to 42.7%) and high homology (88.9%) with the porcine group C VP6 sequence. However, the protein sequence alignments revealed a region of 10 amino acids that were significantly different between the human and the porcine group C viruses.

Molecular analysis of the gene 6 from a porcine group C rotavirus that encodes the NS34 equivalent of group A rotaviruses

The complete nucleotide sequence of the gene 6 from the porcine group (Gp) C rotavirus strain Cowden was determined from gene 6-specific clones selected from a cDNA library and from viral transcript RNA. The gene is 1348 nucleotides in length with a potential initiation codon beginning at nucleotide 25 and a stop codon at nucleotide 1231. The deduced protein contains 402 amino acids. Comparison of the gene 6 from this Gp C strain with sequences in the GenBank data base indicated that this gene shared homology with gene 7 of Gp A rotavirus strain SA-11 (22.9%) and gene 9 of Gp A rotavirus strain UK (22.6%), both of which encode the NS34 protein. In vitro translation products produced from transcripts generated from a gene 6 clone containing the entire open reading frame were not immunoprecipitated with either hyperimmune serum specific for the Gp C Cowden strain or a monoclonal antibody directed against the group antigen (VP6) of the Cowden strain. However, products generated from a full-length gene 5 clone of the Cowden strain were immunoprecipitated by each of these antibodies. These data suggest that in contrast to the Gp A viruses in which the gene 6 encodes the major inner capsid protein VP6, the gene 6 of the Cowden Gp C strain encodes a nonstructural protein corresponding to the NS34 of Gp A rotaviruses.

Comparison of human and porcine group C rotaviruses by northern blot hybridization analysis

The genetic relationship between human and porcine Gp C rotaviruses and between Gp C and Gp A or B rotaviruses was examined by Northern blot hybridization. Cross-hybridization studies using radiolabeled ssRNA transcript probes demonstrated that the human and porcine Gp C rotaviruses shared a high degree of nucleotide sequence homology in most of the eleven gene segments; the greatest sequence divergence was observed in gene 7. Neither the human nor the porcine Gp C probe hybridized strongly with gene segments from Gp A reference strains or a Gp B bovine rotavirus. These data indicate that genetically, porcine and human Gp C rotaviruses are closely related, whereas they are quite distinct from Gp A or B suggesting that porcine and human Gp C rotaviruses may have evolved from a common ancestral source.

Expression of the major inner capsid protein of the group B rotavirus ADRV: primary characterization of genome segment 5

A complete cDNA copy of the fifth RNA segment of the human group B rotavirus, ADRV, has been cloned into plasmid AD512. Gene segment 5 contains 1269 bases and encodes one long open reading frame of 391 amino acids beginning at base 31 and terminating at base 1203. The gene 5 polypeptide, expressed in vitro in a rabbit reticulocyte lysate, comigrates with the 44-kDa major inner capsid protein present on EDTA treated ADRV virions. The gene 5 protein is immunoprecipitable by hyperimmune serum to ADRV, human ADRV convalescent serum and by a group B-specific monoclonal antibody. In addition, this protein shares amino acid identity and similarity with the VP6 proteins from group C and group A rotavirus strains. The ADRV VP6 equivalent protein appears to be more closely related to the group C VP6 than the Group A VP6 polypeptide and a common ancestral rotavirus VP6 precursor protein is suggested. As a result, the fifth RNA segment of ADRV defines the major inner capsid protein, or VP6 equivalent, in the group B rotavirus. Expression of the ADRV VP6 equivalent protein is potentially useful for evaluating the prevalence of serum antibodies to group B rotavirus in human and animal populations as well as for generating antibodies for the direct detection of group B rotavirus antigen.

Sequence conservation of gene 8 between human and porcine group C rotaviruses and its relationship to the VP7 gene of group A rotaviruses

cDNA libraries from porcine group (Gp) C rotavirus strain Cowden and a human Gp C rotavirus strain were generated. The complete nucleotide sequence of gene 8 from the Cowden strain was determined from gene 8-specific clones and viral transcript RNA. A full-length gene 8 clone was generated from the human Gp C virus by polymerase chain reaction (PCR) using primers deduced from the 3' and 5' ends of the Cowden strain gene 8, and the sequence of the human Gp C gene 8 was determined from this clone and gene 8 clones in the cDNA library. The gene 8 from the Cowden or the human Gp C strain is 1063 nucleotides in length and contains a long open reading frame beginning at the 49th nucleotide from the 5' end and terminating with a stop codon 16 bases from the 3' end. The encoded protein contains 332 amino acids (predicted molecular weight of 37.3 kDa) with two potential N-linked glycosylation sites in the porcine strain and three in the human strain. The polypeptide products derived from in vitro translation of the transcript RNA generated from a porcine gene 8 clone containing the entire open reading frame were analogous in size with the Gp A VP7. The gene 8 of porcine and human Gp C rotaviruses exhibited considerable nucleotide and deduced amino acid sequence identity (83.8 and 88.0%, respectively). Comparison of the Gp C gene 8 protein sequence with the VP7 protein of Gp A rotavirus revealed structural similarities, although the overall amino acid identity was low (less than 30%). These data suggest that the gene 8 of the porcine or human Gp C rotavirus encodes a protein corresponding to the VP7 outer capsid glycoprotein of Gp A rotaviruses and that the eighth gene is highly conserved in the porcine and human Gp C strains examined in this study.

Detection of group B and C rotaviruses by polymerase chain reaction

We adapted the polymerase chain reaction (PCR) to detect the noncultivatable group B and C rotaviruses and introduced a simple and convenient technique to purify viral RNA from stool specimens. Double-stranded RNA present in stool extracts was purified by adsorption to hydroxyapatite and was used as the template for reverse transcription and polymerase amplification. Primer pairs specific for group B (gene 8) and group C (gene 6) rotaviruses were selected to amplify group-characteristic sizes of cDNA copies readily identifiable in ethidium bromide-stained agarose gels. These primer pairs were used separately in individual PCR assays or were pooled with a primer pair specific for group A rotavirus (gene 9) in a combined PCR assay for the simultaneous detection of all three rotavirus groups. The method was very sensitive and was used to identify both human and porcine strains of group B and C rotaviruses in stool specimens. A second PCR amplification with internal group-specific primers served to increase further the sensitivity of the test and to confirm the diagnostic results obtained in the first amplification.