The UbiA superfamily is a group of intramembrane prenyltransferases that generate lipophilic compounds essential in biological membranes. These compounds, which include various quinones, hemes, chlorophylls, and vitamin E, participate in electron transport and function as antioxidants, as well as acting as structural lipids of microbial cell walls and membranes. Prenyltransferases producing these compounds are involved in important physiological processes and human diseases. These UbiA superfamily members differ significantly in their enzymatic activities and substrate selectivities. This chapter describes examples of methods that can be used to group these intramembrane enzymes, analyze their activity, and screen and crystallize homolog proteins for structure determination. Recent structures of two archaeal homologs are compared with structures of soluble prenyltransferases to show distinct mechanisms used by the UbiA superfamily to control enzymatic activity in membranes.,? 2017 Elsevier Inc. All rights reserved.