Isolation of a foot-and-mouth disease polyuridylic acid polymerase and its inhibition by antibody

Genomic comparison of foot-and-mouth disease virus R strain and its chick-passaged attenuated strain

The present study examined the genomic differences between foot-and-mouth disease virus (FMDV) R strain and its attenuated, chick-passaged (R(304)) strain. Eleven pairs of primers were used to amplify the complete genome of FMDV R and R(304) by RT-PCR. Each fragment was cloned into pMD18-T vector and sequenced. Nucleotide analyses showed that the genome encoding regions of R and R(304) strains open reading frame (ORF) were both 6966 nucleotides (nt) in length, encoding 2322 amino acids. One hundred and ten nucleotides or 32 amino acids were found to be mutated most frequently were in the 3A gene. The next highest rates of mutation were observed in the LP and 1D genes. No mutations were found in either the 2A or 2C genes. The length of 5'IRES region and 3'UTR were 450 nt and 94 nt, respectively. The 5'IRES region and 3'UTR had only 4 nt and 3 nt mutation, respectively after attenuation. The R(304) poly(A) tail length of 18 nt, while that of the R strain was 30 nt. This result demonstrated the primary genomic changes of a FMDV and its attenuated strain, which has important implications in understanding the molecular epidemiology and functional genomics of FMDV.

Genome analysis and development of infectious cDNA clone of a virulence-attenuated strain of foot-and-mouth disease virus type Asia 1 from China

The RNA genome sequence of the rabbit passage-attenuated strain of foot-and-mouth disease virus (FMDV) Asia 1, ZB/CHA/58(att), was determined to be 8165 nt in length excluding the poly(C) tract in the 5' UTR and the poly(A) tail at the 3' end. ZB/CHA/58(att) was most similar to the vaccine strain Asia 1/YNBS/58 in genome sequence and there were no deletions or insertions within the deduced polyprotein between ZB/CHA/58(att) and YNBS/58, but there were a total of 25 substitutions at the amino acid level and an extra 19-nt stretch in the 5' UTR was found in ZB/CHA/58(att). An infectious full-length cDNA clone of ZB/CHA/58(att) was developed. Infectious virus could be recovered in BHK-21 cells transfected with the synthetic viral RNA transcribed in vitro. The plaque morphology, growth kinetics and antigenic profile of the infectious clone-derived virus (termed tZB) were indistinguishable from those induced by the parental virus. Furthermore, the virulence properties of ZB/CHA/58(att) and tZB were found to be highly similar in the mouse model. The availability of genome sequence information and infectious cDNA clone of the FMDV ZB/CHA/58(att) lays a new ground for further investigation of FMDV virulence determinants and development of new potent vaccine to FMD.

Comparative genomics of foot-and-mouth disease virus

Here we present complete genome sequences, including a comparative analysis, of 103 isolates of foot-and-mouth disease virus (FMDV) representing all seven serotypes and including the first complete sequences of the SAT1 and SAT3 genomes. The data reveal novel highly conserved genomic regions, indicating functional constraints for variability as well as novel viral genomic motifs with likely biological relevance. Previously undescribed invariant motifs were identified in the 5' and 3' untranslated regions (UTR), as was tolerance for insertions/deletions in the 5' UTR. Fifty-eight percent of the amino acids encoded by FMDV isolates are invariant, suggesting that these residues are critical for virus biology. Novel, conserved sequence motifs with likely functional significance were identified within proteins L(pro), 1B, 1D, and 3C. An analysis of the complete FMDV genomes indicated phylogenetic incongruities between different genomic regions which were suggestive of interserotypic recombination. Additionally, a novel SAT virus lineage containing nonstructural protein-encoding regions distinct from other SAT and Euroasiatic lineages was identified. Insights into viral RNA sequence conservation and variability and genetic diversity in nature will likely impact our understanding of FMDV infections, host range, and transmission.

Foot-and-mouth disease

Foot-and-mouth disease (FMD) is a highly contagious disease of cloven-hoofed animals. The disease was initially described in the 16th century and was the first animal pathogen identified as a virus. Recent FMD outbreaks in developed countries and their significant economic impact have increased the concern of governments worldwide. This review describes the reemergence of FMD in developed countries that had been disease free for many years and the effect that this has had on disease control strategies. The etiologic agent, FMD virus (FMDV), a member of the Picornaviridae family, is examined in detail at the genetic, structural, and biochemical levels and in terms of its antigenic diversity. The virus replication cycle, including virus-receptor interactions as well as unique aspects of virus translation and shutoff of host macromolecular synthesis, is discussed. This information has been the basis for the development of improved protocols to rapidly identify disease outbreaks, to differentiate vaccinated from infected animals, and to begin to identify and test novel vaccine candidates. Furthermore, this knowledge, coupled with the ability to manipulate FMDV genomes at the molecular level, has provided the framework for examination of disease pathogenesis and the development of a more complete understanding of the virus and host factors involved.

Molecular basis of pathogenesis of FMDV

Current understanding of the molecular basis of pathogenesis of foot-and-mouth disease (FMD) has been achieved through over 100 years of study into the biology of the etiologic agent, FMDV. Over the last 40 years, classical biochemical and physical analyses of FMDV grown in cell culture have helped to reveal the structure and function of the viral proteins, while knowledge gained by the study of the virus' genetic diversity has helped define structures that are essential for replication and production of disease. More recently, the availability of genetic engineering methodology has permitted the direct testing of hypotheses formulated concerning the role of individual RNA structures, coding regions and polypeptides in viral replication and disease. All of these approaches have been aided by the simultaneous study of other picornavirus pathogens of animals and man, most notably poliovirus. Although many questions of how FMDV causes its devastating disease remain, the following review provides a summary of the current state of knowledge into the molecular basis of the virus' interaction with its host that produces one of the most contagious and frightening diseases of animals or man.

Expression and characterization of the preS1 peptide of hepatitis B surface antigen in Escherichia coli

The infectious particles of hepatitis B virus (HBV) contain 3 related surface antigens, i.e., small, medium, and large, all of which are encoded by one large open reading frame with multiple initiation codons. The large surface antigen (L-Ag) contains preS1, preS2, and S regions while both the middle and small surface antigens lack preS1. Several lines of evidence suggested that the preS1 region is involved in the binding of HBV to human hepatocytes as shown by its binding to HepG2 cells and isolated human hepatocyte membranes. To obtain large quantity of preS1 peptide, an expression vector was constructed containing a lac promoter, the 5' half of the beta-galactosidase gene, the Factor Xa tetrapeptide recognition sequence, and the coding region of preS1 plus preS2. This recombinant plasmid constitutively produced high concentration of a fusion protein in inclusion bodies in Escherichia coli. When the fusion protein was treated with Factor Xa, a peptide consisting of the N-terminal 91 amino acids of the preS1 region was released. This preS1 fragment purified by anion exchange chromatography was able to bind specifically to the isolated plasma membranes from human liver. Hence, this recombinant preS1 peptide can be used to identify and isolate hepatocyte receptors for HBV.

RNA end-labeling and RNA ligase activities can produce a circular rRNA in whole cell extracts from trypanosomes

We have found two enzymatic activities in whole cell extracts from Trypanosoma brucei; an end-labeling reaction involving a single uridine at the 3' end of ribosomal RNAs (rRNAs) and an RNA ligase activity joining 5' monophosphates to 3' hydroxyl groups. The RNA ligase acts upon one of the small rRNAs (180 nucleotides) from the trypanosome ribosomal repeat unit, forming a circular RNA. The specific circularization of this small rRNA is probably dependent on the secondary structure of the molecule and is not detectable in vivo.

Foot-and-mouth disease virus-induced RNA polymerase is associated with Golgi apparatus

Electrophoretic analysis of the Golgi apparatus isolated by differential centrifugation from radiolabeled cells infected with foot-and-mouth disease virus showed about 10 protein bands. The virus-induced RNA polymerase was identified by immunoprecipitation and electron microscope staining procedures. Pulse-chase experiments indicated that the polymerase passed through the Golgi apparatus in less than 1 h.

Indirect immunofluorescence and immunodiffusion tests in the detection of antibodies to foot-and-mouth disease virus

The antibody response detected by indirect immunofluorescence (IIF) as well as that directed against 140 S and virus infection associated antigen (VIA), as detected by agar immunodiffusion, was studied in three mammal species susceptible to Foot and Mouth Disease Virus, after challenge with living virus, immunization and hyperimmunization with inactivated virus, and immunization followed by challenge. By spot indirect immunofluorescence, antibodies were detected only in animals undergoing an active infection, and were not detected in immunized or hyperimmunized animals. This behaviour was similar to that of the anti-VIA antibodies in the same groups of animals and differed from that of anti-140 S antibodies. It appeared that spot indirect immunofluorescence for the detection of VIA antigen is comparable to the immunodiffusion test, but the speed of IIF and the possibility of handling many samples make it more practical.

Sequence of the viral replicase gene from foot-and-mouth disease virus C1-Santa Pau (C-S8)

The nucleotide sequence of the region including the viral replicase gene, the carboxy terminus of protein P18, and the 3'-extracistronic region of foot-and-mouth disease virus (FMDV) type C1-Santa Pau (C-S8) has been determined from previously cloned cDNA fragments [Villanueva et al., Gene 23 (1983) 185-194]. The comparison with the corresponding gene segments of FMDV of serotypes A or O shows base substitutions in 7.2-8.6% of residues in the replicase gene with no insertions or deletions. This is about fourfold lower variation than found for the region encoding capsid protein VP1 of the corresponding viruses. Intermediate variability (substitution at 16.1-23.6% positions) exists in the 3'-extracistronic region, including point mutations, insertions and deletions. The predicted amino acid sequence of the replicase gene indicates that 75.5-82.6% of mutations are silent and that 93.4% of amino acids are conserved in the four FMDV replicases. The frequency of certain types of silent mutations and of rare codon usage is significantly lower for the replicase gene than for the protein VP1 coding region.

Correlation of surface and internal ultrastructural changes in cells infected with foot-and-mouth disease virus

The surfaces of primary and continuous line cell cultures displayed the same sequence of morphological changes during the course of infection with foot-and-mouth disease virus. These changes could be classified into four broad stages: I) cells were flattened, closely attached to one another and microvilli appeared, II) cells rounded, microvilli began to disappear and the cells started to separate from one another by cytoplasmic strands, III) cells were discrete, rounded structures and IV) cells were rounded and had numerous attached buds, some of which contained virus. The internal changes included the appearance of increasing amounts of smooth membranous vacuoles lined with the viral induced RNA polymerase and the presence of buds, some with viral particles inside. While the different cell cultures showed similar internal and external changes as a result of infection, they responded to infection at different rates and contained subpopulations of resistant cells.

Identification of amino acid and nucleotide sequence of the foot-and-mouth disease virus RNA polymerase

Foot-and-mouth disease virus (FMDV) RNA polymerase was purified from the polyethylene glycol (PEG)-treated supernatant of infected cell media by a combination of ion-exchange chromatography, membrane molecular filtration, and affinity chromatography. The purified RNA polymerase which migrated as a single band of 56,000 molecular weight on a polyacrylamide gel was subjected to automated Edman degradation and the sequence of the first 30 amino acid residues established. On the basis of previous evidence, which indicated that the RNA polymerase was the most 3'-translated polypeptide, plasmids containing cDNA mapping at the 3' end of the genome were characterized by restriction enzyme analysis and nucleotide sequencing. These investigations definitively established the derived amino acid sequence by confirmation of 28 of the amino terminal residues determined by amino acid sequence analysis; the location of the FMDV RNA polymerase coding region at the extreme 3' end of the genome, 96 nucleotides from the poly(A) tail; and the N-terminal cleavage point of the RNA polymerase from its precursor P100 was found to be a glutamic acid-glycine bond.

Ultrastructural changes and antigen localization in tissues from foot-and-mouth disease virus-infected guinea-pigs

Foot-and-mouth disease virus (FMDV)-induced ultrastructural changes in guinea-pig tongue, heelpad, mammary and liver tissues were examined using scanning and transmission electron microscopy. FMDV infection caused cell rounding and the release of virus in membrane limited vesicles in the animal tissues similar to that seen in other work in cell cultures. Microfilaments were present which may be responsible for cell rounding. Immunoperoxidase labeling revealed the attachment of the virus-infection associated (VIA) antigen to the smooth vacuoles of mammary and liver tissues, and to milk fat globules. The electron microscope immunoperoxidase procedure increased the sensitivity of detection sufficiently to allow the visualization of VIA antigen in tissues not previously shown to have the antigen. It is postulated that the release of the smooth vacuoles from the liver cells stimulates the animal's immune response to the VIA antigen.

Localization of foot-and-mouth disease--RNA synthesis on newly formed cellular smooth membranous vacuoles

Viral RNA synthesis in foot-and-mouth disease infected bovine kidney cell cultures was associated throughout the infectious period with newly formed smooth membranous vacuoles. Membrane formation was measured by choline uptake. The site of RNA synthesis was determined by electron microscopic examination of autoradiograms of incorporated [3H] uridine. Both membrane formation and RNA synthesis became significant at 2.5 hours postinfection, but membrane formation increased steadily to 4.5 hours while RNA synthesis peaked at 3.5 hours. Percent density distributions of developed silver grains on autoradiograms showed that almost all RNA synthesis was concentrated on the smooth vacuoles of infected cells. Histogram analysis of grain density distributions established that the sites of RNA synthesis was the vacuolar membrane. The newly formed smooth membrane-bound vacuoles were not seen to coalesce into the large vacuolated areas typical of poliovirus cytopathogenicity.

Biochemical evidence of recombination within the unsegmented RNA genome of aphthovirus

Four different pairs of temperature-sensitive mutants, derived from the same strain of aphthovirus, were crossed by using an infectious center recombination test. Each parental mutant carried an unselected marker affecting the isoelectric point of a virus-coded polypeptide; progeny of the crosses, able to grow at the nonpermissive temperature, were screened for these unselected markers. Polypeptide charge was shown to be a stable, inheritable character, and three of the four crosses yielded genetic recombinants that possessed the polypeptide marker from both parents. Peptide fingerprinting and high-resolution isoelectric focusing of the polypeptides ruled out the explantation that these viruses were generated by mutation.

Characterization of a 70S polyuridylic acid polymerase isolated from foot-and-mouth disease virus-infected cells

A polyuridylic acid polymerase complex isolated from foot-and-mouth disease virus-infected cells sedimented at 70S in a sucrose gradient and appeared in the exclusion volume of an agarose column whose molecular weight cutoff was 5 x 10(6). Phenol extraction of the complex yielded a heterogeneous band of virus-specific RNA and an apparently host cell-derived 4.5 to 5S RNA, both of which are essentially single stranded. Neither RNA served as a template in the cell-free enzyme reaction. Polyacrylamide gel analysis revealed five polypeptides with molecular weights of 50,000, 56,000, 60,000, 70,000, and 74,000 and with molar ratios of 1:2:2:1:1, respectively. Autoradiography showed P56 to be the only major virus-induced polypeptide; the other proteins are apparently of host cell origin. Electron microscopic examination suggested a cartwheel shape for the polymerase complex which was seen to dissociate as polyadenylic acid was added. Antibody previously shown to inhibit enzyme activity aggregated the 70S units.

Temperature-sensitive RNA polymerase mutants of a picornavirus

Temperature-sensitive (ts) RNA polymerase mutants of a picornavirus are reported. Two foot-and-mouth disease virus (FMDV) mutants designated ts 22 and ts 115 have been characterized. As judged by isoelectric focusing, both have charge alterations in P56a, the FMDV RNA polymerase protein. Virus RNA synthesis in cells infected with the mutants is severely impaired at the nonpermissive temperature. RNA polymerase purified from baby hamster kidney cells infected with these mutants exhibits a marked ts transcribing activity in vitro. Spontaneous revertants of both mutants have P56a polypeptides that are indistinguishable from the parental proteins on the basis of charge. The revertants regain the ability to synthesize virus RNA in vivo at the nonpermissive temperature. RNA polymerase purified from the revertants remains transcriptionally active at the nonpermissive temperature.

Biochemistry of Theiler's murine encephalomyelitis virus isolated from acutely infected mouse brain: identification of a previously unreported polypeptide

The WW strain of Theiler's murine encephalomyelitis virus (WW-TMEV) was purified from homogenates of acutely infected mouse brain. Infectious WW-TMEV was found to have an estimated sedimentation coefficient of 156 (s20,w) and a density of 1.35 g/cm3 in CsCl. Electron microscopy revealed a homogeneous population of 26-nm nonenveloped particles. Iodination of sodium dodecyl sulfate (SDS)-disrupted virions revealed four major capsid proteins with molecular weights of 58,000, 37,000, 34,000, and 27,000. A 6,000-dalton polypeptide was observed after long exposures of autoradiograms. The 37,000-, 24,000-, 27,000-, and 6,000-dalton polypeptides corresponded to picornaviral VP1, VP2, VP3, and VP4 capsid polypeptides, respectively. Comparison of autoradiograms of virions radiolabeled before and after SDS disruption indicated that the 58,000-dalton protein, VP2, and VP3 preferentially bound 125I under the labeling conditions used. Direct evidence was obtained that VP2 and VP3 were derived from the 58,000-dalton polypeptide by isolation of the 58,000-dalton polypeptide from polyacrylamide gels run under nonreducing conditions and subjecting it to reelectrophoresis under reducing conditions. The effect of trypsin on purified virions and their polypeptides was also investigated. Trypsin-sensitive sites were found in the 58,000-dalton protein, VP1, and VP2. Our results indicate that, in addition to the four typical picornaviral capsid polypeptides, there is a 58,000-dalton polypeptide present in WW-TMEV, which is sensitive to trypsin and can be reduced into two of the capsid proteins, VP2 and VP3.