CORRECTION OF STRUCTURE FACTORS OF SINGLE PARTICLE IMAGES

Baylor College Of Medicine, Houston TX

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Abstract

For single particles, it is impractical to record electron diffraction intensities. We are developing a strategy to make corrections of the amplitudes and phases of the structure factors computed from electron images of single particles. Our computational procedure of summing the Fourier transforms of the single particle images has proven effective in determining the zeros of the contrast transfer function and thus the defocus value of the image. This defocus determination is used to correct the phase reversal of the structure factors. For the amplitudes, we attempted to use x ray solution scattering to determine the scattering profile of the particles with which we would correct for the amplitudes of the computed structure factors. The x-ray data has been collected at the Stanford Linear Accelerator Laboratory with the assistance of Hiro Tsuruta. Initially, we collected low angle solution scattering data in the range of 300 to 50 [unreadable]using a multi-layer crystal and then high angle data in the range of 100 to 5 [unreadable]. Subsequently, we used a better positionally calibrated Si(111) monochromator crystal for data collection at resolution ranges from 400 to 13 [unreadable] and from 50 to 4 [unreadable]. Using these data, we are able to determine quantitatively the amount of amplitude contrast and the extent of damping in the computed transforms of our 400 keV images P22 phages. These parameters will be corrected in our final reconstruction in order to obtain a more accurate structure.