Production Of Defective Interfering Particles Research Articles

A novel phosphoserine motif in the LCMV matrix protein Z regulates the release of infectious virus and defective interfering particles.

We report that the lymphocytic choriomeningitis virus (LCMV) matrix protein, which drives viral budding, is phosphorylated at serine 41 (S41). A recombinant (r)LCMV bearing a phosphomimetic mutation (S41D) was impaired in infectious and defective interfering (DI) particle release, while a non-phosphorylatable mutant (S41A) was not. The S41D mutant was disproportionately impaired in its ability to release DI particles relative to infectious particles. Thus, DI particle production by LCMV may be dynamically regulated via phosphorylation of S41.

The Lymphocytic Choriomeningitis Virus Matrix Protein PPXY Late Domain Drives the Production of Defective Interfering Particles.

Arenaviruses cause severe diseases in humans but establish asymptomatic, lifelong infections in rodent reservoirs. Persistently-infected rodents harbor high levels of defective interfering (DI) particles, which are thought to be important for establishing persistence and mitigating virus-induced cytopathic effect. Little is known about what drives the production of DI particles. We show that neither the PPXY late domain encoded within the lymphocytic choriomeningitis virus (LCMV) matrix protein nor a functional endosomal sorting complex transport (ESCRT) pathway is absolutely required for the generation of standard infectious virus particles. In contrast, DI particle release critically requires the PPXY late domain and is ESCRT-dependent. Additionally, the terminal tyrosine in the PPXY motif is reversibly phosphorylated and our findings indicate that this posttranslational modification may regulate DI particle formation. Thus we have uncovered a new role for the PPXY late domain and a possible mechanism for its regulation.

Population dynamics of an RNA virus and its defective interfering particles in passage cultures

BackgroundViruses can fall prey to their defective interfering (DI) particles. When viruses are cultured by serial passage on susceptible host cells, the presence of virus-like DI particles can cause virus populations to rise and fall, reflecting predator-prey interactions between DI and virus particles. The levels of virus and DI particles in each population passage can be determined experimentally by plaque and yield-reduction assays, respectively.ResultsTo better understand DI and virus particle interactions we measured vesicular stomatitis virus and DI particle production during serial-passage culture on BHK cells. When the multiplicity of infection (MOI, or ratio of infectious virus particles to cells) was fixed, virus yields followed a pattern of progressive decline, with higher MOI driving earlier and faster drops in virus level. These patterns of virus decline were consistent with predictions from a mathematical model based on single-passage behavior of cells co-infected with virus and DI particles. By contrast, the production of virus during fixed-volume passages exhibited irregular fluctuations that could not be described by either the steady-state or regular oscillatory dynamics of the model. However, these irregularities were, to a significant degree, reproduced when measured host-cell levels were incorporated into the model, revealing a high sensitivity of virus and DI particle populations to fluctuations in available cell resources.ConclusionsThis study shows how the development of mathematical models, when guided by quantitative experiments, can provide new insight into the dynamic behavior of virus populations.

Segment-specific noncoding sequences of the influenza virus genome RNA are involved in the specific competition between defective interfering RNA and its progenitor RNA segment at the virion assembly step.

The generation of influenza A virus defective interfering (DI) particles was studied by using an NS2 mutant which produces, in a single cycle of virus replication, a large amount of DI particles lacking the PA polymerase gene. The decrease in PA gene replication has been shown to occur primarily at the cRNA synthesis step, with preferential amplification of PA DI RNA species present in a marginal amount in the virus stock. In addition, at the assembly step the PA DI RNAs were preferentially incorporated into virions, resulting in selective reduction in the packaging of the PA gene into virions. Similarly, in cells dually infected with the NS2 mutant and wild-type viruses, packaging of the wild-type PA gene was also greatly suppressed. In contrast, incorporation of other RNA segments, i.e., the PB2 and NS genes, was not affected, suggesting that the PA DI RNAs competed only with the PA gene in a segment-specific manner. Experiments involving rescue of recombinant chloramphenicol acetyltransferase (CAT) RNA flanked by the noncoding regions of the PA (PA/CAT RNA) and PB2 (PB2/CAT RNA) genes into viral particles showed that only PA/CAT RNA was not rescued by infection with the NS2 mutant virus containing the PA DI RNAs. However, recombinant PA/CAT RNA in which either the 3' or 5' noncoding region was replaced with that of the PB2 gene was rescued by the NS2 mutant. These results suggest that the noncoding regions of the PA gene are responsible for the competition with PA DI RNA species at the virus assembly step and that coexistence of the both noncoding regions would be a prerequisite for this phenomenon. Decreased packaging of the progenitor RNA by the DI RNA, in addition to the suppression of cRNA synthesis, is likely involved in the production of DI particles.

In vitro construction of poliovirus defective interfering particles

To construct poliovirus defective interfering (DI) particles in vitro, we synthesized an RNA from a cloned poliovirus cDNA, pSM1(T7)1, which carried a deletion in the genome region corresponding to nucleotide positions 1663 to 2478 encoding viral capsid proteins, by using bacteriophage T7 RNA polymerase. The RNA was designed to retain the correct reading frame in nucleotide sequence downstream of the deletion. HeLa S3 monolayer cells were transfected with the deletion RNA and then superinfected with standard virus as a helper. The DI RNA was observed in the infected cells after three passages at high multiplicity of infection. The sequence analysis of RNA extracted from the purified DI particle clearly showed that this DI RNA had the same deletion in size and location as that in the RNA used for the transfection. Thus, we succeeded in construction of a poliovirus DI particle in vitro. To gain insight into the mechanism for DI generation, we constructed poliovirus cDNAs pSM1(T7)1a and pSM1(T7)1b that, in addition to the same deletion as that in pSM1(T7)1, had insertion sequences of 4 bases and 12 bases, respectively, at the corresponding nucleotide position, 2978. The RNA transcribed from pSM1(T7)1a was not a template for synthesis of poliovirus nonstructural proteins and therefore was inactive as an RNA replicon. On the other hand, the RNA from pSM1(T7)1b replicated properly in the transfected cells. Superinfection of the transfected cells with standard virus resulted in production of DI particles derived from pSM1(T7)1b and not from pSM1(T7)1a. These observations indicate that deletion RNAs that are inactive replicons have little or no possibility of being genomes of DI particles suggesting the existence of a nonstructural protein(s) that has an inclination to function as a cis-acting protein(s). The method described here will provide a useful technique to investigate genetic information essential for poliovirus replication.

Regeneration of DI particles of virulent and attenuated rabies virus: genome characterization and lack of correlation with virulence phenotype.

Two strains of fixed rabies virus were examined for their ability to regenerate defective interfering (DI) particles and for possible correlation of DI particle production with the expression of virulence. A plaque-purified stock of the attenuated ERA strain (ERApp), which characteristically caused an auto-interfering death response in adult mice inoculated i.c., was serially passed at a high m.o.i. inBHK-21 cells. By the sixth passage, DI particles were regenerated that corresponded in sedimentation velocity and DI/RNA size to the smallest of three sizes of DI particles produced by the parental stock virus. The regeneration of ERA DI particles in vivo was not detected during 15 serial high or low m.o.i. passages of infected newborn mouse brain, though the passaged virus consistently elicited an auto-interfering-type death response when assayed in adult mice. The attenuated Flury HEPpp strain regenerated up to three unique size classes of DI particles during serial passage in BHK-21 or murine neuroblastoma C1300 clone NA cells compared with the one band of DI particles produced by the parental Flury HEP stock virus. The BHK-21 cell-adapted Flury HEPpp virus failed to kill adult mice when inoculated at high concentrations after two serial passages in NA cells. However, the virus became fully virulent and a single band of regenerated DI particles was visible. Additional bands of defective particles were visible following the third serial passage in NA cells. Single-stranded RNA with a mol. wt. of 0.62 x 10(6) was extracted from the first DI particle population to be regenerated. This corresponded in mol. wt. to the DI/ssRNA characteristic of the parental attenuated Flury HEP virus. However, in the parental type DI/RNA, partially dsRNA could be isolated in addition to ssRNA. Double-stranded RNA could not be detected in the regenerated DI particles derived from the virulent NA cell-propagated Flura HEPpp virus. These results suggest that the virulence phenotype of fixed rabies viruses does not depend on the presence or absence of DI particles.

Ringed Plaque Formation in Infectious Pancreatic Necrosis Virus Correlates with Defective Interfering Particle Production

SUMMARY Four isolates of infectious pancreatic necrosis virus showed ringed plaque morphology on chinook salmon embryo cells, while six other isolates showed clear plaque morphology. One isolate chosen from the ringed-plaque class yielded defective interfering (DI) particles after as few as two virus passages starting with plaque-purified material; another isolate from the clear-plaque class failed to yield detectable numbers of DI particles.

Comparison of vesicular stomatitis virus defective interfering particle synthesis in chick embryo and L cells

A comparison of the ability of vesicular stomatitis virus (VSV) to generate and replicate defective interfering (DI) particles in primary chick embryo (CE) and mouse L cells was investigated as a means of analyzing host control over DI-particle synthesis and interfering capacity. Serial undiluted passage of VSV in CE and L cells indicate that VSV-DI particles are generated and (or) replicate with greater efficiency in CE than in L cells. When DI particles accumulate in L cells, they are able to interfere with infectious particle replication. The DI particles from CE cells interfered to the same extent with infectious particle replication in both CE and L cells. L cells, therefore, are not considered 'low-interference' hosts in which DI particles are produced and do not interfere with infectious virus replication, but rather hosts which restrict the production of DI particles.

Characterization of rabies viruses recovered from persistently infected BHK cells

Persistent rabies virus infection with a cyclic rising and falling pattern was easily initiated in BHK cells. In striking contrast with the same chronic infection established by T. J. Wiktor and H. F. Clark ((1972). Infect. Immun. 6, 988–995), this virus and cell interaction was not mediated by interferon, and the infected cells were not resistant to a heterologous virus challenge. The persistently infected cells produced small-plaque viruses (SPV) and, after a number of subcultures, these SPV replaced entirely the wild large-plaque viruses (LPV). Due to the marked cytopathic effects (CPE) on BHK cells, SPV was less efficient than LPV for the establishment of viral persistence. A fraction containing defective interfering (DI) rabies virus particles was obtained by density gradient centrifugation of virus stocks from the persistently infected cells. The DI particles could be quantitatively assayed to the degree that they suppressed the CPE by the standard rabies virus. Cyclic production of DI particles in the persistent infection was demonstrated by this method. This evidence plus the fact that the homologous virus resisted superinfection indicate that the DI particles of rabies virus play a major role in the establishment and maintenance of a persistent state of infection in vitro.