Small G proteins are molecular switches in cellular signal transduction. Many small G proteins that we are studying, such as Ras and Ral, are involved in oncogenesis and those in the Rho family, such as Cdc42 and Rac are important for invasion and metastasis. We are using a combination of structural biology and biochemical techniques to understand protein-protein interactions in the complexes formed between small G proteins and their downstream effectors. An understanding of these interactions will be crucial to the design of drugs that target these complexes. Furthermore, targetting a single effector interaction is useful for studying pathways in vivo. We are also interested in understanding how effector proteins downstream of small G proteins are modulated by their interaction with the G protein.