METHOD TO DETERMINE HEAVY-ATOM POSITIONS FOR VIRUS STRUCTURES

Small spherical virus particles consist of multiples of 60 chemically identical protein subunits related to icosahedral symmetry. If the orientation of the virus is previously established, then Patterson self-vectors can be calculated between heavy atoms attached specifically to equivalent points in each subunit. A systematic search of all reasonable positions within the subunit and a comparison with the known difference Patterson map would establish heavy-atom positions relative to the particle center. This method was used successfully on 2 heavy-atom derivatives of satellite tobacco necrosis virus.