EM Tomography Core (Jensen. Director: Tivol & Ding. Managers) Overview The EM Tomography Core will be housed within the Jensen lab at the California Institute of Technology in Pasadena, California. Two electron cryomicroscopes are present there: a 300kV, FEG, liquid heliumcooled, energy filtered, dual-axis tilting, fully automated G2 Polara, and a 120 kV, LaB6, liquid nitrogencooled Tecnai T12. The EM Tomography Core produces 3D reconstrucfions of unique samples such as individual virions or cells to macromolecular (~2-6 nm) resolution. Two cryoelectron microscopes are used, a 300-kV Polara and a 120- kV T12, both from the FEI Company. Samples are either plunge-frozen intact in liquid ethane or high-pressure frozen and then cryosecfioned. Tilt-series are acquired automafically and then combined computafionally to produce the 3-D reconstrucfions.