Mechanism Of Genome Packaging Research Articles

Electron microscopic analysis of viral assembly and budding

Viruses show ultrastructural changes during viral assembly and budding processes in which viral genome and proteins are systemically assembled. Electron microscopy is the only way that enables us to observe such ultrastructural changes. We have investigated the mechanisms of Ebola and influenza virion formation by electron microscopy. We have elucidated the roles of each Ebola virus protein in viral assembly and budding as well as the mechanisms of genome packaging of influenza A viruses.

Biochemical and structural characterization of Cren7, a novel chromatin protein conserved among Crenarchaea.

Archaea contain a variety of chromatin proteins consistent with the evolution of different genome packaging mechanisms. Among the two main kingdoms in the Archaea, Euryarchaeota synthesize histone homologs, whereas Crenarchaeota have not been shown to possess a chromatin protein conserved at the kingdom level. We report the identification of Cren7, a novel family of chromatin proteins highly conserved in the Crenarchaeota. A small, basic, methylated and abundant protein, Cren7 displays a higher affinity for double-stranded DNA than for single-stranded DNA, constrains negative DNA supercoils and is associated with genomic DNA in vivo. The solution structure and DNA-binding surface of Cren7 from the hyperthermophilic crenarchaeon Sulfolobus solfataricus were determined by NMR. The protein adopts an SH3-like fold. It interacts with duplex DNA through a β-sheet and a long flexible loop, presumably resulting in DNA distortions through intercalation of conserved hydrophobic residues into the DNA structure. These data suggest that the crenarchaeal kingdom in the Archaea shares a common strategy in chromatin organization.

Viral capsids: Mechanical characteristics, genome packaging and delivery mechanisms

.The main functions of viral capsids are to protect, transport and deliver their genome. The mechanical properties of capsids are supposed to be adapted to these tasks. Bacteriophage capsids also need to withstand the high pressures the DNA is exerting onto it as a result of the DNA packaging and its consequent confinement within the capsid. It is proposed that this pressure helps driving the genome into the host, but other mechanisms also seem to play an important role in ejection. DNA packaging and ejection strategies are obviously dependent on the mechanical properties of the capsid. This review focuses on the mechanical properties of viral capsids in general and the elucidation of the biophysical aspects of genome packaging mechanisms and genome delivery processes of double-stranded DNA bacteriophages in particular.

How retroviruses select their genomes

As retroviruses assemble in infected cells, two copies of their full-length, unspliced RNA genomes are selected for packaging from a cellular milieu that contains a substantial excess of non-viral and spliced viral RNAs. Understanding the molecular details of genome packaging is important for the development of new antiviral strategies and to enhance the efficacy of retroviral vectors used in human gene therapy. Recent studies of viral RNA structure in vitro and in vivo and high-resolution studies of RNA fragments and protein-RNA complexes are helping to unravel the mechanism of genome packaging and providing the first glimpses of the initial stages of retrovirus assembly.

Packaging the replicon RNA of the Far-Eastern subtype of tick-borne encephalitis virus into single-round infectious particles: development of a heterologous gene delivery system

The sub-genomic replicon of tick-borne encephalitis (TBE) virus (Far-Eastern subtype) was packaged into infectious particles by providing the viral structural proteins in trans. Sequential transfection of TBE replicon RNA and a plasmid that expressed the structural proteins led to the secretion of infectious particles that contained TBE replicon RNA. The secreted particles had single-round infectivity, which was inhibited by TBE virus-neutralizing antibody. The physical structure of the particles was almost identical to that of infectious virions, and the packaged replicon RNA showed no recombination with the mRNAs of the viral structural proteins. Furthermore, heterologous genes were successfully delivered and expressed by packaging TBE replicon RNA with inserted GFP and Neo genes. This replicon packaging system may be a useful tool for the molecular study of the TBE virus genome packaging mechanism, and for the development of vaccine delivery systems.

Yeast virology

The three families of double-stranded RNA (dsRNA) viruses and two families of retroviruses (retrotransposons) of the yeast Saccharomyces cerevisiae are all transmitted between cells only by cell fusion, probably reflecting the high frequency of mating of yeast cells in nature. One dsRNA virus and two retroviruses apparently use ribosomal "frameshifting" to produce major coat protein-polymerase fusion proteins. This mechanism allows regulation of the relative amounts of major coat protein and fusion protein that are made and avoids the possibility of mutant virus genomes being generated by splicing. Moreover, the fusion protein structure suggests a possible mechanism of genome packaging. The recent development of in vitro replication, transcription, and integration systems for these viruses, and the ease with which classical genetic and molecular studies are executed in yeast, are yielding detailed information about the roles of cellular and viral components in the viral replication cycles and the host defensive response. A host defense system against yeast dsRNA viruses is known and there is evidence to suggest a system active against the retroviruses.