K2 summit direct electron detect camera

The cryo-EM specimens were imaged on a Titan Krios transmission electron microscope (Thermo Fisher - FEI, Hillsboro, OR). The electron images were recorded using a K2 Summit direct electron detect camera (Gatan, Pleasanton, CA) in super-resolution counting mode. Image collection was automated with SerialEM (Fiedor et al., 2008 (link)) utilizing scripting of stage shifts between hole exposures. The defocus was set to vary between 0.8 and 2.6 μm, corresponding to a super-resolution pixel size of 0.525 Å at the specimen level. The counting rate was adjusted to 7.614 e⁻/Ų s. Total exposure time was 8 s accumulating to a dose of 61 e⁻/Ų.

Imaging of FRL-PSI was performed on a Titan Krios G2 transmission electron microscope (Thermo Fisher Scientific/FEI, Hillsboro, OR). Images were recorded on a K2 Summit direct electron detect camera (Gatan, Pleasanton, CA) in super-resolution mode. The defocus varied from −1 to −3 μm, and the nominal magnification was 47,600, corresponding to a super-resolution pixel size of 0.53 Å at the specimen level. The counting rate was adjusted to 7.166 e⁻ pixel⁻¹ s⁻¹. The total exposure time was 8 s, accumulating to a dose of 57.328 e⁻ Å⁻². In total, 6593 micrograph images were collected. SerialEM automated data collection using the K2 Summit and Titan Krios GS resulted in 3692 LZW-compressed tiff movie files (43 (link)).