ELECTRON-DIFFRACTION OF HELICAL PARTICLES

The development of low-dose electron cryo-microscopy has provided the means to see structural details to better than 10 Angstrom resolution in helical structures. The application of techniques of image analysis to micrographs can yield accurate phases, but not amplitudes with whi ch to generate three-dimensional maps of the structure. Electron diffr action can provide reliable amplitudes, which can be combined with the phases from the images. In order to collect amplitude data, two probl ems have to be overcome: the pattern should be obtained from a large w ell ordered sample of particles, and the inelastic background should b e properly subtracted. In this paper, we present three simple methods to produce rafts of helical particles. Using these methods we have obt ained electron diffraction patterns from TMV (with data out to 0.28 nm ), TMV protein stacked disks (with data out to 0.3 nm) and bacterial f lagellar filaments (with data out to 0.5 nm). In addition, we describe the algorithms used to extract the amplitudes from the diffraction pa tterns.