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Estimates of the Fourier Amplitude Decay of Electron Micrographs of Single Particles

Published online by Cambridge University Press:  02 July 2020

Ali Saad
Affiliation:
National Center for Macromolecular Imaging, Baylor College of Medicine, Houston, Texas77030, USA;
Steven J. Ludtke
Affiliation:
National Center for Macromolecular Imaging, Baylor College of Medicine, Houston, Texas77030, USA;
Joanita Jakana
Affiliation:
National Center for Macromolecular Imaging, Baylor College of Medicine, Houston, Texas77030, USA;
Frazer J. Rixon
Affiliation:
Medical Research Council Virology Unit, Institute of Virology, GlasgowG11 5JR, Scotland
Hiro Tsuruta
Affiliation:
SSRL/SLAC, Stanford University, P.O. Box 4349, Stanford, CA94309, USA
Wah Chiu
Affiliation:
National Center for Macromolecular Imaging, Baylor College of Medicine, Houston, Texas77030, USA;
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Several structures of single particles have been resolved to 7-9 Å using electron cryomicroscopy. This field is now poised to make the next step, to near atomic (3-4 Å) resolution. Signal to noise ratio is the critical factor determining the amount of data required for a structural determination at higher resolution. When properly weighted, signal to noise ratio is additive as image data is averaged coherently, however, this relies on perfect alignment of the noisy images. Typical refinement algorithms require as high a signal to noise ratio as possible for accurate alignment. We report a method, which allows accurate, routine determination of signal to noise ratio and other image parameters, both for data quality assessment and microscope quality tracking.

Figure la shows a typical 400 kV electron image of ice-embedded herpesvirus capsids. The incoherent sum of the Fourier transforms of particle images (Fig. lb) shows that the data contains information out to a resolution of 7 Å. When rotationally averaged, this power spectrum can be expressed as:

Type
Electron Cryomicroscopy of Macromolecules
Copyright
Copyright © Microscopy Society of America

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