REPLICATION OF POLIOVIRUS RNA INDUCED BY HETEROLOGOUS VIRUS

In pursuit of intriguing puzzles

This Invited Review is a kind of scientific autobiography based on the presentation at the Symposium "Viruses: Discovering Big in Small" held in honor of the author's 90th birthday (Moscow, March 2019).

Emergency Services of Viral RNAs: Repair and Remodeling

Reproduction of RNA viruses is typically error-prone due to the infidelity of their replicative machinery and the usual lack of proofreading mechanisms. The error rates may be close to those that kill the virus. Consequently, populations of RNA viruses are represented by heterogeneous sets of genomes with various levels of fitness. This is especially consequential when viruses encounter various bottlenecks and new infections are initiated by a single or few deviating genomes. Nevertheless, RNA viruses are able to maintain their identity by conservation of major functional elements. This conservatism stems from genetic robustness or mutational tolerance, which is largely due to the functional degeneracy of many protein and RNA elements as well as to negative selection. Another relevant mechanism is the capacity to restore fitness after genetic damages, also based on replicative infidelity. Conversely, error-prone replication is a major tool that ensures viral evolvability. The potential for changes in debilitated genomes is much higher in small populations, because in the absence of stronger competitors low-fit genomes have a choice of various trajectories to wander along fitness landscapes. Thus, low-fit populations are inherently unstable, and it may be said that to run ahead it is useful to stumble. In this report, focusing on picornaviruses and also considering data from other RNA viruses, we review the biological relevance and mechanisms of various alterations of viral RNA genomes as well as pathways and mechanisms of rehabilitation after loss of fitness. The relationships among mutational robustness, resilience, and evolvability of viral RNA genomes are discussed.

Evidence for an enterovirus as the cause of encephalitis lethargica

BACKGROUND

The epidemic of encephalitis lethargica (EL), called classical EL, was rampant throughout the world during 1917-1926, affecting half a million persons. The acute phase was lethal for many victims. Post-encephalitic parkinsonism (PEP) affected patients for decades. Our purpose was to investigate the cause of classical EL by studying the few available brain specimens. Cases of PEP and modern EL were also studied. Transmission electron microscopy (TEM) and immunohistochemistry were employed to examine brain from four classical EL cases, two modern EL cases and one PEP case.

METHODS

Standard methods for TEM, immunohistochemistry and RTPCR were applied.

RESULTS

27 nm virus-like particles (VLP) were observed in the cytoplasm and nuclei of midbrain neurons in all classical EL cases studied. Large (50 nm) VLP and 27 nm intranuclear VLP were observed in the modern EL cases and the PEP case. Influenza virus particles were not found. VLP were not observed in the control cases. TEM of cell cultures inoculated with coxsackievirus B4 and poliovirus revealed both small and large intranuclear virus particles and small cytoplasmic particles, similar to the VLP in EL neurons. In the EL brains, nascent VLP were embedded in putative virus factories and on endoplasmic reticulum (ER). The VLP in the cases of classical EL survived, whereas ribosomes underwent autolysis due to the lack of refrigeration and slow formaldehyde fixation of whole brain. The VLP were larger than ribosomes from well preserved brain. Immunohistochemistry of classical EL cases using anti-poliovirus and anti-coxsackievirus B polyclonal antibodies showed significant staining of cytoplasm and nuclei of neurons as well as microglia and neuropil. Purkinje cells were strongly stained.A 97-bp RNA fragment of a unique virus was isolated from brain tissue from acute EL case #91558. Sequence analysis revealed up to 95% identity to multiple human Enteroviruses. Additional cases had Enterovirus positive reactions by real time PCR.

CONCLUSIONS

The data presented here support the hypothesis that the VLP observed in EL tissue is an Enterovirus.

Tyrosine 3 of poliovirus terminal peptide VPg(3B) has an essential function in RNA replication in the context of its precursor protein, 3AB

Poliovirus (PV) VPg is a genome-linked protein that is essential for the initiation of viral RNA replication. It has been well established that RNA replication is initiated when a molecule of UMP is covalently linked to the hydroxyl group of a tyrosine (Y3) in VPg by the viral RNA polymerase 3D(pol), but it is not yet known whether the substrate for uridylylation in vivo is the free peptide itself or one of its precursors. The aim of this study was to use complementation analyses to obtain information about the true in vivo substrate for uridylylation by 3D(pol). Previously, it was shown that a VPg mutant, in which tyrosine 3 and threonine 4 were replaced by phenylalanine and alanine (3F4A), respectively, was nonviable. We have now tested whether wild-type forms of proteins 3B, 3BC, 3BCD, 3AB, 3ABC, and P3 provided either in trans or in cis could rescue the replication defect of the VPg(3F4A) mutations in the PV polyprotein. Our results showed that proteins 3B, 3BC, 3BCD, and P3 were unable to complement the RNA replication defect in dicistronic PV or dicistronic luciferase replicons in vivo. However, cotranslation of the P3 precursor protein allowed rescue of RNA replication of the VPg(3F4A) mutant in an in vitro cell-free translation-RNA replication system, but only poor complementation was observed when 3BC, 3AB, 3BCD, or 3ABC proteins were cotranslated in the same assay. Interestingly, only protein 3AB but not 3B and 3BC, when provided in cis by insertion of a wild-type 3AB coding sequence between the P2 and P3 domains of the polyprotein, supported the replication of the mutated genome in vivo. Elimination of cleavage between 3A and 3B in the complementing 3AB protein, however, led to a complete lack of RNA replication. Our results suggest that (i) VPg has to be delivered to the replication complex in the form of a large protein precursor (P3) to be fully functional in replication; (ii) the replication complex formed during PV replication in vivo is essentially inaccessible to proteins provided in trans, even if the complementing protein is translated from a different cistron of the same RNA genome; (iii) 3AB is the most likely precursor of VPg; and (iv) Y3 of VPg has an essential function in RNA replication in the context of both VPg and 3AB.

Effect of inactivation by hydroxylamine on early functions of poliovirus

Evidence is presented that poliovirus particles with a single lethal hit by hydroxylamine do not induce in host cells either inhibition of cellular protein synthesis or viral ribonucleic acid (RNA) replication. The RNA of these viruses is not replicated even if the cells are simultaneously infected with both active and inactivated viruses. The damaged viral RNA seems to have lost both its template function and its function in the translation of normal viral proteins.

The specific effectors of viral development

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