Selection, packaging and delivery of nucleic acids are important steps in the virus life cycle. The same principles are being exploited in gene therapy by delivering the foreign genes to the target cells. Organization of nucleic acids in viruses helps to understand their role in virus assembly, stability and perhaps the release of the nucleic acid during the cell entry stage. However, the packaged nucleic acids in the viral capsids can not be seen at high resolution unlike the capsid protein subunits, because the packaged nucleic acid does not strictly conform to the icosahedral symmetry. The same is true with the regions of the capsid protein that interact closely with the RNA. The so called """"""""disordered regions"""""""" at high resolution, however, can be detected at low resolution (1000-10 E) as broad envelopes of density that define approximately the location of the polypeptides. Low resolution diffraction data sets were collected, at SSRL BL 4-2, on the crystals of authentic Flock House Virus (aFHV) particles packaging viral RNAs and baculo expressed (synthetic) Flock House Virus (sFHV) particles packaging heterologous RNAs. The electron density maps of aFHV and sFHV calculated between 300-14 E resolution revealed the distribution of the packaged nucleic acids. Although the overall RNA distribution in aFHV and sFHV are similar due to imposed icosahedral symmetry, there are clear differences in their organization: viral RNA in aFHV appeared to be more structured and interacts closely with the protein capsid; RNA.
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