Highlights d Structure of SARS-CoV-2 replication-transcription complex (RTC) with nsp13 helicases d The nsp13 NTPase domains sit in front of the RCT, constraining functional models d Nsp13 may drive RTC backtracking, affecting proofreading and template switching d Structural analysis of ADP-Mg 2+-bound NiRAN domain, a potential antiviral target

We present an approach for preparing cryoEM grids to study short-lived molecular states. Using piezo electric dispensing, two independent streams of ~50 pL sample drops are deposited within 10 ms of each other onto a nanowire EM grid surface, and the mixing reaction stops when the grid is vitrified in liquid ethane, ~100 ms later. We demonstrate this approach for four biological systems where short-lived states are of high interest.

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Cryo–electron microscopy (cryo-EM) continues its remarkable growth as a method for visualizing biological objects, which has been driven by advances across the entire pipeline. Developments in both single-particle analysis and in situ tomography have enabled more structures to be imaged and determined to better resolutions, at faster speeds, and with more scientists having improved access. This review highlights recent advances at each stage of the cryo-EM pipeline and provides examples of how these techniques have been used to investigate real-world problems, including antibody development against the SARS-CoV-2 spike during the recent COVID-19 pandemic. Expected final online publication date for the Annual Review of Biochemistry, Volume 91 is June 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.