Small angle scattering study of the structure and organization of RNA and protein in Brome Mosaic Virus (BMV)*

Brome mosaic virus (BMV) is a small icosahedral of the alpha virus-like superfamily of RNA with a segmented positive-strand RNA genome and a mean diameter $\sim $ 268{\AA} that offers high levels of RNA synthesis and virus production in plants. BMV also tightly regulates the packaging of its four RNAs (RNA1 through RNA4) into three separate particles; RNA1 and RNA2 are encapsidated separately while one copy each of RNA3 and RNA4 are normally packaged together. Small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS) were applied to study the size, shape and protein-RNA organization of BMV. D$_{2}$O/H$_{2}$O mixture was used to enhance contrast in SANS measurement. The radial distribution of BMV from the Fourier transform of scattering spectrum gives a clear indication of RNA packing, and distribution and their structure in the BMV. The result reveals that the virus is about 266 {\AA} in diameter and is composed of RNA inside the virion coated with a protein shell.