Cryo-electron tomography was performed as described45 (link) using a Polara Tecnai G2 Transmission electron microscope (FEI Company, Hillsboro, OR, USA) equipped with a 4 × 4 K CCD camera at the end of an energy filter (Gatan Inc., Pleasanton). Tilt series were recorded with either 1° or 2° increments between ±60° with a total dose of 150–180 e−/Å2. Tilt series were imaged with a 200 kV beam at a −3 μm defocus and × 34 K magnification, with a pixel size of 3.9 Å at the sample plane. The pixel size at the reported imaging conditions was measured using catalase crystal and cross grating calibration grids as standards (EMS, Hatfield, PA, USA).
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