Yeast membraneless compartments revealed by correlative light microscopy and electron tomography

Yeast essential enzymes are able to assemble and form membrane-less compartments in the cytoplasm during stress conditions (Narayanaswamy et al., 2009). These microcompartments form rapidly under ATP-depletion upon cellular regulation of pH and molecular crowding (Munder et al., 2016). So far, the behavior of most of these enzymes has been characterized by live imaging using fluorescence microscopy. The ultrastructure of only a few enzymes in the assembled form has been solved, thus revealing their capacity of forming highly ordered self-assemblies (Barry et al., 2014; Petrovska et al., 2014; Prouteau et al., 2017). Here we show how we used correlative light and electron microscopy (CLEM) and transmission electron tomography (ET) to reveal the in situ arrangement adopted by the yeast enzyme eIF2B (eukaryotic translation initiation 2B) in its compartmentalized form upon energy depletion.