Aggregation-associated loss of antigenicity observed for denatured virion protein 1 of Equine rhinitis A virus in an enzyme-linked immunosorbent assay.

Equine rhinitis A virus (ERAV) is a picornavirus which causes an acute respiratory infection in horses worldwide, and virus neutralization (VN) has been the standard method for the detection of ERAV antibody in horse serum. Previous studies have identified recombinant virion protein VP1 (rVP1) purified under native conditions to be of high potential for the development of a diagnostic ERAV enzyme-linked immunosorbent assay (ELISA). This study presents an optimized protocol for the expression and purification of native full-length rVP1. Furthermore, we demonstrate that, upon denaturation, rVP1 no longer reacts to ERAV antibody in a prototype ELISA. Size exclusion chromatography (SEC) performed on native and denatured rVP1 indicates that denatured rVP1 forms multimeric aggregates that may causally connect to the loss of antigenicity observed in the ELISA.

Root cause investigation of a viral contamination incident occurred during master cell bank (MCB) testing and characterization--a case study.

An adventitious agent contamination occurred during a routine 9 CFR bovine viral screening test at BioReliance for an Eli Lilly Chinese Hamster Ovary (CHO) cell-derived Master Cell Bank (MCB) intended for biological production. Scientists from the sponsor (Eli Lilly and Company) and the testing service company (BioReliance) jointly conducted a systematic investigation in an attempt to determine the root cause of the contamination. Our investigation resulted in the identification of the viral nature of the contaminant. Subsequent experiments indicated that the viral contaminant was a non-enveloped and non-hemadsorbing virus. Transmission electron microscopy (TEM) revealed that the viral contaminant was 25-30 nm in size and morphologically resembled viruses of the family Picornaviridae. The contaminant virus was readily inactivated when exposed to acidic pH, suggesting that the viral contaminant was a member of rhinoviruses. Although incapable of infecting CHO cells, the viral contaminant replicated efficiently in Vero cell with a life cycle of approximately 16 h. Our investigation provided compelling data demonstrating that the viral contaminant did not originate from the MCB. Instead, it was introduced into the process during cell passaging and a possible entry point was proposed. We identified the viral contaminant as an equine rhinitis A virus using molecular cloning and DNA sequencing. Finally, our investigation led us to conclude that the source of the viral contaminant was the equine serum added to the cell growth medium in the 9 CFR bovine virus test.

Evidence for an RNA chaperone function of polypyrimidine tract-binding protein in picornavirus translation.

The cellular polypyrimidine tract-binding protein (PTB) is recruited by the genomic RNAs of picornaviruses to stimulate translation initiation at their internal ribosome entry site (IRES) elements. We investigated the contribution of the individual RNA recognition motif (RRM) domains of PTB to its interaction with the IRES of foot-and-mouth disease virus (FMDV). Using a native gel system, we found that PTB is a monomer, confirming recent reports that challenged the previous view that PTB is a dimer. Mapping the spatial orientation of PTB relative to the bound IRES RNA, we found that the two C-terminal RRM domains III and IV of PTB bind in an oriented way to the IRES. Domain III contacts the IRES stem-loop 2, while domain IV contacts the separate IRES 3' region. PTB domain I appears not to be involved directly in RNA binding, but domain II stabilizes the RNA binding conferred by domains III and IV. A PTB protein containing only these two C-terminal PTB domains is sufficient to enhance the entry of initiation factor eIF4G to the IRES and stimulate IRES activity, and the long-lived PTB-IRES interaction stabilized by domain II is not a prerequisite for this function. Thus, PTB most likely acts as an RNA chaperone to stabilize IRES structure and, in that way, augment IRES activity.

Subcellular distribution of the foot-and-mouth disease virus 3A protein in cells infected with viruses encoding wild-type and bovine-attenuated forms of 3A.

Picornavirus infection induces the proliferation and rearrangement of intracellular membranes in response to the synthesis of nonstructural proteins, including 3A. We have previously shown that changes in 3A are associated with the inability of a Taiwanese strain of foot-and-mouth disease virus (FMDV) (OTai) to grow in bovine cells and cause disease in cattle, although the virus grows to high titers in porcine cells and is highly virulent in pigs (C. W. Beard and P. W. Mason, 2000, J. Virol. 74, 987-991). To study if differences in the distribution of 3A could account for the species specificity of OTai, we compared the localization of the OTai 3A with a bovine-virulent 3A (serotype A12) in keratinocytes prepared from the tongues of cattle and pigs. Following either infection of keratinocytes or transfection with 3A we were unable to discern differences in 3A distribution in either species of keratinocyte, independent of the strain of virus (or 3A) utilized. In both cell types, 3A distributed in a pattern that overlapped with an endoplasmic reticulum (ER) marker protein, calreticulin (CRT). Furthermore, although FMDV infection or transfection with 3A did not result in a gross redistribution of CRT, both virus infection and 3A transfection disrupted the Golgi. Other picornaviruses that disrupt Golgi function are sensitive to brefeldin A (BFA), a fungal metabolite that interferes with retrograde transport between the Golgi and the ER. Interestingly, BFA has little effect on FMDV replication, suggesting that FMDV may acquire cellular membranes into its replication complexes in a manner different from that of other picornaviruses.

Foot-and-mouth disease virus can utilize the C-terminal extension of coxsackievirus A9 VP1 for cell infection.

Foot-and-mouth disease virus (FMDV) is known to employ the conserved Arg-Gly-Asp (RGD) tripeptide located on the variable betaG-betaH loop of the VP1 capsid protein for binding to cells. Coxsackievirus A9 (CAV9) also carries an RGD sequence, but on a short C-terminal extension of its VP1 and in a different amino acid context. This apparent relationship raised the question of whether insertion of the heterologous CAV9 sequence into FMDV would influence infection by the genetically modified FMDV. Four VP1 mutants were generated by PCR mutagenesis of a full-length FMDV cDNA plasmid. After transfection of BHK-21 cells, viral protein synthesis and virus particle formation could be detected. Two of the four mutants, mV9b and mV9d, could be propagated in BHK-21 cells, but not in CV-1 cells. Both of these mutants contained 17 amino acids of the C terminus of CAV9 VP1. Infection of BHK cells could be specifically inhibited by rabbit immune serum raised against a synthetic peptide representing the amino acid sequence of the C-terminal extension of CAV9 VP1. This demonstrated the direct involvement of the inserted sequence in cell infection. In fact, genetically modified FMDV O(1)K was capable of employing the VP1 C-terminal RGD region of CAV9 for infection of BHK cells. In addition, these results show that, even in cell culture-adapted viruses, the RGD-containing betaG-betaH loop plays an important role in virus infectivity.

Role of the cytoplasmic domain of the beta-subunit of integrin alpha(v)beta6 in infection by foot-and-mouth disease virus.

Field isolates of foot-and-mouth disease virus (FMDV) are believed to use RGD-dependent integrins as cellular receptors in vivo. Using SW480 cell transfectants, we have recently established that one such integrin, alpha(v)beta6, functions as a receptor for FMDV. This integrin was shown to function as a receptor for virus attachment. However, it was not known if the alpha(v)beta6 receptor itself participated in the events that follow virus binding to the host cell. In the present study, we investigated the effects of various deletion mutations in the beta6 cytoplasmic domain on infection. Our results show that although loss of the beta6 cytoplasmic domain has little effect on virus binding, this domain is essential for infection, indicating a critical role in postattachment events. The importance of endosomal acidification in alpha(v)beta6-mediated infection was confirmed by experiments showing that infection could be blocked by concanamycin A, a specific inhibitor of the vacuolar ATPase.

Analysis of the aphthovirus 2A/2B polyprotein 'cleavage' mechanism indicates not a proteolytic reaction, but a novel translational effect: a putative ribosomal 'skip'.

The 2A region of the aphthovirus foot-and-mouth disease virus (FMDV) polyprotein is only 18 aa long. A 'primary' intramolecular polyprotein processing event mediated by 2A occurs at its own C terminus. FMDV 2A activity was studied in artificial polyproteins in which sequences encoding reporter proteins flanked the 2A sequence such that a single, long, open reading frame was created. The self-processing properties of these artificial polyproteins were investigated and the co-translational 'cleavage' products quantified. The processing products from our artificial polyprotein systems showed a molar excess of 'cleavage' product N-terminal of 2A over the product C-terminal of 2A. A series of experiments was performed to characterize our in vitro translation systems. These experiments eliminated the translational or transcriptional properties of the in vitro systems as an explanation for this imbalance. In addition, the processing products derived from a control construct encoding the P1P2 region of the human rhinovirus polyprotein, known to be proteolytically processed, were quantified and found to be equimolar. Translation of a construct encoding green fluorescent protein (GFP), FMDV 2A and beta-glucuronidase, also in a single open reading frame, in the presence of puromycin, showed this antibiotic to be preferentially incorporated into the [GFP2A] translation product. We conclude that the discrete translation products from our artificial polyproteins are not produced by proteolysis. We propose that the FMDV 2A sequence, rather than representing a proteolytic element, modifies the activity of the ribosome to promote hydrolysis of the peptidyl(2A)-tRNA(Gly) ester linkage, thereby releasing the polypeptide from the translational complex, in a manner that allows the synthesis of a discrete downstream translation product to proceed. This process produces a ribosomal 'skip' from one codon to the next without the formation of a peptide bond.

The 'cleavage' activities of foot-and-mouth disease virus 2A site-directed mutants and naturally occurring '2A-like' sequences.

The 2A/2B cleavage of aphtho- and cardiovirus 2A polyproteins is mediated by their 2A proteins 'cleaving' at their own C termini. We have analysed this activity using artificial reporter polyprotein systems comprising green fluorescent protein (GFP) linked via foot-and-mouth disease virus (FMDV) 2A to beta-glucuronidase (GUS) -- forming a single, long, open reading frame. Analysis of the distribution of radiolabel showed a high proportion of the in vitro translation products (approximately 90%) were in the form of the 'cleavage' products GUS and [GFP2A]. Alternative models have been proposed to account for the 'cleavage' activity: proteolysis by a host-cell proteinase, autoproteolysis or a translational effect. To investigate the mechanism of this cleavage event constructs encoding site-directed mutant and naturally occurring '2A-like' sequences were used to program in vitro translation systems and the gel profiles analysed. Analysis of site-directed mutant 2A sequences showed that 'cleavage' occurred in constructs in which all the candidate nucleophilic residues were substituted -- with the exception of aspartate-12. This residue is not, however, conserved amongst all functional '2A-like' sequences. '2A-like' sequences were identified within insect virus polyproteins, the NS34 protein of type C rotaviruses, repeated sequences in Trypanosoma spp. and a eubacterial alpha-glucosiduronasesequence(Thermatoga maritima aguA). All of the 2A-like sequences analysed were active (to various extents), other than the eubacterial alpha-glucosiduronase 2A-like sequence. This method of control of protein biogenesis may well not, therefore, be confined to members of the PICORNAVIRIDAE: Taken together, these data provide additional evidence that neither FMDV 2A nor '2A-like' sequences are autoproteolytic elements.

Type-independent detection of foot-and-mouth disease virus by monoclonal antibodies that bind to amino-terminal residues of capsid protein VP2.

The characterization of monoclonal antibodies raised against the foot-and-mouth disease virus isolates A22 Iraq/1964, Asia1 Shamir-Israel/1989, and SAT1 Zimbabwe/1989 with regard to neutralizing activity and sensitivity of their epitopes for treatment with trypsin, resulted in the identification of one non-neutralizing antibody in each panel that binds to a trypsin-sensitive epitope. Furthermore, each of these antibodies recognized 27 isolates of different provenance, representative of six serotypes. These antibodies are recommended for type-independent antigen detection by ELISA. The epitopes for these antibodies reside at the intertypically conserved N-terminus of capsid protein VP2. The two are specified by the lysines at positions two and three, but differ from each other as indicated by the variable heavy chain sequences of their antibodies.

High-efficiency utilization of the bovine integrin alpha(v)beta(3) as a receptor for foot-and-mouth disease virus is dependent on the bovine beta(3) subunit.

We have previously reported that Foot-and-mouth disease virus (FMDV), which is virulent for cattle and swine, can utilize the integrin alpha(v)beta(3) as a receptor on cultured cells. Since those studies were performed with the human integrin, we have molecularly cloned the bovine homolog of the integrin alpha(v)beta(3) and have compared the two receptors for utilization by FMDV. Both the alpha(v) and beta(3) subunits of the bovine integrin have high degrees of amino acid sequence similarity to their corresponding human subunits in the ectodomains (96%) and essentially identical transmembrane and cytoplasmic domains. Within the putative ligand-binding domains, the bovine and human alpha(v) subunits have a 98.8% amino acid sequence similarity while there is only a 93% similarity between the beta(3) subunits of these two species. COS cell cultures, which are not susceptible to FMDV infection, become susceptible if cotransfected with alpha(v) and beta(3) subunit cDNAs from a bovine or human source. Cultures cotransfected with the bovine alpha(v)beta(3) subunit cDNAs and infected with FMDV synthesize greater amounts of viral proteins than do infected cultures cotransfected with the human integrin subunits. Cells cotransfected with a bovine alpha(v) subunit and a human beta(3) subunit synthesize viral proteins at levels equivalent to those in cells expressing both human subunits. However, cells cotransfected with the human alpha(v) and the bovine beta(3) subunits synthesize amounts of viral proteins equivalent to those in cells expressing both bovine subunits, indicating that the bovine beta(3) subunit is responsible for the increased effectiveness of this receptor. By engineering chimeric bovine-human beta(3) subunits, we have shown that this increase in receptor efficiency is due to sequences encoding the C-terminal one-third of the subunit ectodomain, which contains a highly structured cysteine-rich repeat region. We postulate that amino acid sequence differences within this region may be responsible for structural differences between the human and bovine beta(3) subunit, leading to more efficient utilization of the bovine receptor by this bovine pathogen.

The epithelial integrin alphavbeta6 is a receptor for foot-and-mouth disease virus.

Field isolates of foot-and-mouth disease virus (FMDV) have been shown to use the RGD-dependent integrin alphavbeta3 as a cellular receptor on cultured cells. However, several other RGD-dependent integrins may have the potential to act as receptors for FMDV in vivo. Of these, alphavbeta6 is a likely candidate for use as a receptor by FMDV as it is expressed on epithelial cells, which correlates with the tissue tropism of the virus. In this report, we show that human colon carcinoma cells (SW480) that are normally nonpermissive for FMDV become susceptible to infection as a result of transfection with the integrin beta6 subunit and expression of alphavbeta6 at the cell surface. Integrin alphavbeta6 is the major site for virus attachment on the beta6-transfected cells, and binding to alphavbeta6 serves to increase the rate of virus entry into these cells. In addition, we show that virus binding and infection of the beta6-transfected cells is mediated through an RGD-dependent interaction that is specifically inhibited by a monoclonal antibody (10D5) that recognizes alphavbeta6. These studies establish a role for alphavbeta6 as a cellular receptor for FMDV.

Foot-and-mouth disease virus is a ligand for the high-affinity binding conformation of integrin alpha5beta1: influence of the leucine residue within the RGDL motif on selectivity of integrin binding.

Field isolates of foot-and-mouth disease virus (FMDV) use RGD-dependent integrins as receptors for internalization, whereas strains that are adapted for growth in cultured cell lines appear to be able to use alternative receptors like heparan sulphate proteoglycans (HSPG). The ligand-binding potential of integrins is regulated by changes in the conformation of their ectodomains and the ligand-binding state would be expected to be an important determinant of tropism for viruses that use integrins as cellular receptors. Currently, alphavbeta3 is the only integrin that has been shown to act as a receptor for FMDV. In this study, a solid-phase receptor-binding assay has been used to characterize the binding of FMDV to purified preparations of the human integrin alpha5beta1, in the absence of HSPG and other RGD-binding integrins. In this assay, binding of FMDV resembled authentic ligand binding to alpha5beta1 in its dependence on divalent cations and specific inhibition by RGD peptides. Most importantly, binding was found to be critically dependent on the conformation of the integrin, as virus bound only after induction of the high-affinity ligand-binding state. In addition, the identity of the amino acid residue immediately following the RGD motif is shown to influence differentially the ability of FMDV to bind integrins alpha5beta1 and alphavbeta3 and evidence is provided that alpha5beta1 might be an important FMDV receptor in vivo.

Cell recognition by foot-and-mouth disease virus that lacks the RGD integrin-binding motif: flexibility in aphthovirus receptor usage.

Cell surface molecules that can act as virus receptors may exert an important selective pressure on RNA viral quasispecies. Large population passages of foot-and-mouth disease virus (FMDV) in cell culture select for mutant viruses that render dispensable a highly conserved Arg-Gly-Asp (RGD) motif responsible for integrin receptor recognition. Here, we provide evidence that viability of recombinant FMDVs including a Asp-143-->Gly change at the RGD motif was conditioned by a number of capsid substitutions selected upon FMDV evolution in cell culture. Multiply passaged FMDVs acquired the ability to infect human K-562 cells, which do not express integrin alpha(v)beta(3). In contrast to previously described cell culture-adapted FMDVs, the RGD-independent infection did not require binding to the surface glycosaminoglycan heparan sulfate (HS). Viruses which do not bind HS and lack the RGD integrin-binding motif replicate efficiently in BHK-21 cells. Interestingly, FMDV mutants selected from the quasispecies for the inability to bind heparin regained sensitivity to inhibition by a synthetic peptide that represents the G-H loop of VP1. Thus, a single amino acid replacement leading to loss of HS recognition can shift preferential receptor usage of FMDV from HS to integrin. These results indicate at least three different mechanisms for cell recognition by FMDV and suggest a potential for this virus to use multiple, alternative receptors for entry even into the same cell type.

Interaction of eukaryotic initiation factor eIF4B with the internal ribosome entry site of foot-and-mouth disease virus is independent of the polypyrimidine tract-binding protein.

Eukaryotic translation initiation factor 4B (eIF4B) binds directly to the internal ribosome entry site (IRES) of foot-and-mouth disease virus (FMDV). Mutations in all three subdomains of the IRES stem-loop 4 reduce binding of eIF4B and translation efficiency in parallel, indicating that eIF4B is functionally involved in FMDV translation initiation. In reticulocyte lysate devoid of polypyrimidine tract-binding protein (PTB), eIF4B still bound well to the wild-type IRES, even after removal of the major PTB-binding site. In conclusion, the interaction of eIF4B with the FMDV IRES is essential for IRES function but independent of PTB.

The structure and function of a foot-and-mouth disease virus-oligosaccharide receptor complex.

Heparan sulfate has an important role in cell entry by foot-and-mouth disease virus (FMDV). We find that subtype O1 FMDV binds this glycosaminoglycan with a high affinity by immobilizing a specific highly abundant motif of sulfated sugars. The binding site is a shallow depression on the virion surface, located at the junction of the three major capsid proteins, VP1, VP2 and VP3. Two pre-formed sulfate-binding sites control receptor specificity. Residue 56 of VP3, an arginine in this virus, is critical to this recognition, forming a key component of both sites. This residue is a histidine in field isolates of the virus, switching to an arginine in adaptation to tissue culture, forming the high affinity heparan sulfate-binding site. We postulate that this site is a conserved feature of FMDVs, such that in the infected animal there is a biological advantage to low affinity, or more selective, interactions with glycosaminoglycan receptors.

C-terminal region of VP1 of selected foot-and-mouth disease virus serotypes: expression in E. coli and affinity purification.

Foot-and-mouth disease (FMD), one of the most contagious and economically important diseases of farm animals, is caused by a FMD virus (FMDV) which belongs to the family of Picornaviridae. The virus occurs as seven serotypes of which four (A, O, C and Asia 1) are prevalent in India. Immunoprophylaxis supported by precise diagnosis is the prime requirement for achieving the success in controlling the disease. Recently, recombinant DNA technology is gaining importance for the production of cost-effective and safer diagnostics and immunogens. Based on this approach, cDNA of a part of gene for major variable immunogenic region, VP1, of FMDV of four serotypes (A22, O, C and Asia 1) was amplified by PCR and cloned into expression vector. The expression of the 16 K protein gene from the clones was induced with IPTG and analyzed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS-PAGE) and [35S]-methionine labeling. The immunoreactivity of the labeled proteins was assayed by immunoprecipitation with anti-FMDV type-specific sera. Since the proteins contain 6 His residues at the N-terminal end, their affinity purification was carried out using nickel nitrilo-tri-acetic acid (Ni-NTA) agarose matrix. The proteins were found to be immunoreactive and the useful in the FMD diagnosis.

Parameters influencing translational efficiency in aphthovirus IRES-based bicistronic expression vectors.

Initiation of translation in picornavirus RNAs occurs internally, mediated by an internal ribosome entry site (IRES) element. This property has been exploited to coexpress proteins from a single bicistronic transcription unit in eukaryotic cells. The region that separates the IRES element from the authentic initiator codon of the second gene plays an important role in the translation efficiency of this cistron. In the present report, we have analyzed the effect of sequence modifications in this region on the translation efficiency directed by the foot-and-mouth disease (FMDV) IRES in bicistronic expression vectors. Insertion of various sequences, which contained additional start codons and/or the capacity to form hairpins immediately downstream of the 3' border of the IRES, strongly reduced the translation efficiency of the second gene in bicistronic RNAs. Interestingly, an increase of distance per se did not have a deleterious effect on translation efficiency. The bicistronic vector studied here tolerated 95 nucleotides between the 3' border of the IRES and the authentic start codon, provided that out-of-frame AUG codons or hairpins were not present in this RNA segment. These results indicate that FMDV-derived bicistronic constructs are extremely well suited for use in eukaryotic expression vectors.

Conformational flexibility in a highly mobile protein loop of foot-and-mouth disease virus: distinct structural requirements for integrin and antibody binding.

The G-H loop of foot-and-mouth disease virus VP1 protein is a highly mobile peptide, that extends from the capsid surface and that in native virions is invisible by X-ray crystallography. In serotype C, this segment contains a hypervariable region with several continuous, overlapping, B-cell epitopes that embrace the conserved Arg-Gly-Asp (RGD) cell attachment motif. The solvent-exposed positioning of this peptide by selective insertion into different structural frameworks of E. coli beta-galactosidase, generates a spectrum of antigenic variants which react distinctively with a panel of anti-VP1 monoclonal antibodies and exhibit different efficiencies as cell ligands. The cell attachment efficiency is much less restricted by the different positioning of the viral segment at the insertion sites. A molecular model of an inserted stretch reveals a highest flexibility of the RGD tripeptide segment compared with the flanking sequences, that could allow a proper accommodation to integrin receptors even in poorly antigenic conformations. The non-converging structural requirements for RGD-mediated integrin binding and antibody recognition, explains the dynamism of the generation of neutralisation-resistant antigenic variants in the viral quasi-species, arising from a conformational space of integrin-binding competent peptides. This might be of special relevance for foot-and-moth disease virus evolution, since unlike in other picornaviruses, the cell binding motif and the major neutralising B-cell epitopes overlap in a solvent-exposed peptide accessible to the host immune system, in a virion lacking canyons and similar hiding structures.

Multiple virulence determinants of foot-and-mouth disease virus in cell culture.

Hypervirulent variants of foot-and-mouth disease virus (FMDV) of serotype C arise upon serial cytolytic or persistent infections in cell culture. A specific mutation in the internal ribosome entry site of persistent FMDV was previously associated with enhanced translation initiation activity that could contribute to the hypervirulent phenotype for BHK-21 cells. Here we report that several hypervirulent FMDV variants arising upon serial cytolytic passage show an invariant internal ribosome entry site but have a number of mutations affecting structural and nonstructural viral proteins. The construction of chimeric type O-type C infectious transcripts has allowed the mapping of a major determinant of hypervirulence to the viral capsid. Tissue culture-adapted FMDV displayed enhanced affinity for heparin, but binding to cell surface heparan sulfate moieties was not required for expression of the hypervirulent phenotype in Chinese hamster ovary (CHO) cells. Virulence was identical or even higher for glycosaminoglycan-deficient CHO cells than for wild-type CHO cells. FMDV variants with decreased affinity for heparin were selected from a high-binding parental population and analyzed. Substitutions associated with decreased heparin binding were located at positions 173 of capsid protein VP3 and 144 of capsid protein VP1. These substitutions had a moderate effect on virulence for BHK-21 cells but completely abrogated infection of CHO cells. The comparative results with several FMDV isolates show that (i) increased affinity for heparin and alterations in cell tropism may be mediated by a number of independent sites on the viral capsid and (ii) the same capsid modifications may have different effects on different cell types.

[Physico-chemical bases of the mechanism of thermal inactivation of the foot-and-mouth disease virus]. / Fiziko-khimicheskie osnovy mekhanizma termoinaktivatsii virusa iashchura.

Experiments demonstrated that the effect of water activity on the solvate complex of virions underlies the mechanism of thermal inactivation of the foot and mouth disease virus in suspension; changes in the structure of the complex impair the electrophysical balance of the RNA-protein relations and hence, destroy the virus. Heating of virus-containing suspensions at moderate positive temperatures leads to destruction of the noninfectious part of virus population of 146S particles, thus decreasing the infectious activity of the virus.