An x-ray scattering study of bromegrass mosaic virus.

X-ray scattering data and electron microscope observations are presented for bromegrass mosaic virus. Its radial density distribution is obtained from the Fourier transform of the amplitudes of the scattered x-rays. The results indicate that the virus is 260 A in diameter, it has an almost empty central cavity which is about 80 A in diameter, and the regions occupied by RNA and protein are approximately equal in average density. Electron micrographs of negatively stained preparations also give an outside diameter of 260 A and indicate that there is a central region about 90 A in diameter into which uranyl acetate can penetrate. Positively stained preparations indicate that the nucleic acid is concentrated in a shell-shaped region which is in turn surrounded by a shell of protein. In order for the RNA and protein regions to have the same average electron density the RNA must have a hydration of 1.29 gm of water per gm of RNA and the protein must have a hydration of 0.24 gm of water per gm of protein.