From Configuration to Activities of Viral vector RNA Complex Formation

Awad Habiba^*
*Correspondence: Awad Habiba, Rice Research Department, Field Crops Research Institute, Agricultural Research Center, Giza, Egypt, Email:

Introduction

Retroviruses bundle two homologous copies of their genomic RNA during the late phase of their replication cycle to form infectious viral particles. In order to generate new viral particles, the dimerization signal inside the 5′-region of the viral genome and the viral Gag precursor greatly promote this co-packaging of gRNA molecules. The process of genome dimerization is extremely conserved among retroviruses, and it is required for numerous key phases in the retroviral life cycle. For starters, gRNA dimerization is required for selective genome packing by various retroviruses, including the human immunodeficiency virus type 1 and the murine leukaemia virus.

Second, RNA dimerization-induced structural changes may influence translation of unspliced gRNA. Third, during reverse transcription, dimerization of the viral genome is critical because it allows genome repair via strand transfer when one of the two RNA strands is broken. Finally, genome dimerization has the benefit of permitting genetic recombination during reverse transcription, which increases genetic diversity. Even though a tetrameric arrangement of the genome had been hypothesised, ultracentrifugation sedimentation analysis of gRNA isolated Rous sarcoma virus provided the first evidence for the existence of a dimeric genome.

About the Study

Following that, sedimentation and electron microscopy analyses confirmed the genome's dimeric organisation, and this observation was extended to other retrovirus families such as alpharetro viruses, gammaretro viruses, and lentiviruses, revealing the conservation and importance of gRNA dimerization in retrovirus life cycles. Further research revealed that the areas involved in gRNA dimerization, known as the dimer linkage structure, are often near to the 5′-end of gRNA and highly organised, with many stem-loop motifs. Despite the vast size of retroviral genomes, gRNA dimerization was shown to be mediated by short regions spanning from 50 to a few hundreds of nucleotides.

DLS-containing RNA segments dimerized in the presence of monovalent and divalentcations in vitro at temperatures ranging from 37 to 60°C, depending on the virus. The discovery of the HIV-1 dimerization initiating site, on the other hand, provided a clearer knowledge of the exact processes driving the dimerization process.

The inclusion of at least one short palindromic sequence allowing intermolecular base-pairing and hence generating kissing-loop structures is a frequent characteristic of retroviral DIS. Chemical modification interference tests permitted the discovery of the six nucleotides that make up the DIS in HIV-1. Kissing-loop complexes, also known as "loose dimers," have a limited thermal stability and can only be detected via gel electrophoresis at native circumstances, as even mild denaturing conditions dissolve RNA dimers during migration.

Incubation of DLS-containing RNAs at non-physiologically high temperatures (50-60°C) was discovered to cause the creation of RNA dimers that were resistant to mild-denaturing electrophoresis conditions, which were dubbed "tight dimers." Importantly, tight dimers may be formed in the presence of the analogous nucleocapsid protein, which is well-known for its RNA chaperone characteristics. These findings support the hypothesis that NC decreases energy barriers and promotes gRNA refolding into a more stable shape. These conformational modifications might include the refolding of these structures by producing cruciform intermediates that develop into extended intermolecular base-pairing, according to studies on short sequences containing the DIS.

In vivo, immature virions go through a maturation process that is required for viral infectivity and is mediated by the viral protease, which cleaves the viral Pr55Gag and Pr160GagPol precursors into mature structural and enzymatic proteins. The viral genome goes through a maturation phase at the same time as the proteolytic maturation. Indeed, gRNA dimers isolated from juvenile HIV- 1 and MuLV virions are less stable than those retrieved from adult virions. The various stabilities reported in immature and mature virions are strikingly comparable to those observed in vitro for loose and tight RNA dimers, implying that these conformations may represent the development of gRNA into viral particles [1-5].

Conclusion

In this review, we will discuss our current understanding of the processes and molecular variables involved in gRNA dimerization for several retrovirus families in vitro and in cellula, as well as its significance during the retroviral life cycle and its potential targeting by antiviral agents.

References

1. Dubois, Noé, Roland Marquet, Jean-Christophe Paillart, and Serena Bernacchi. "Retroviral RNA dimerization: from structure to functions." Front Microbiol 9 (2018): 527.

Google Scholar, Crossref, Indexed at

2. Skripkin, Eugene, Jean-Christophe Paillart, Roland Marquet, and Bernard Ehresmann, et al. "Identification of the primary site of the human immunodeficiency virus type 1 RNA dimerization in vitro." Proc Nat Aca of Sci 91(1994): 4945-4949.

Google Scholar, Crossref

3. Moore, Michael D., and Wei-Shau Hu. "HIV-1 RNA dimerization: It takes two to tango."AIDS Rev 11(2009): 91.

Google Scholar

4. Paillart, Jean-Christophe, Lionel Berthoux, Michele Ottmann, and Jean-Luc Darlix, et al. "A dual role of the putative RNA dimerization initiation site of human immunodeficiency virus type 1 in genomic RNA packaging and proviral DNA synthesis." J Virol 70 (1996): 8348-8354.

Google Scholar

5. Marquet, Roland, Florence Baudin, Caroline Gabus, and Jean-Luc Darlix, et al. "Dimerization of human immunodeficiency virus RNA: Stimulation by cations and possible mechanism." Nucleic Acids Res 19 (1991): 2349-2357.

Google Scholar, Crossref