The ER is a vast network that includes different domains with different functions. The rough ER is made of ribosome covered membrane sheets and is involved in protein translation.  The smooth ER consists of tubules and is important for lipid synthesis and Ca2+ transport. In his second talk, Rapoport explains how his lab identified several families of proteins needed to generate and maintain a tubular ER network. Using ultra-thin section microscopy, Rapoport and others also showed that stacked ER sheets are held together by helicoidal membrane connections that form a “parking-garage” like structure.