G Proteins is an introduction to one class of systems used for signal transduction at the cell surface, with emphasis on its utilization of a heterotrimeric GTP-binding protein (G protein) to mediate the transfer of information across the plasma membrane, from receptor to effector. Topics covered include the structure and function of G-protein α chains, ADP-ribosylation factor of adenylyl cyclase, and G protein-mediated effects on ionic channels. The organization of genes coding for G-protein α subunits in higher and lower eukaryotes is also discussed. This book is comprised of 25 chapters and begins with an overview of G proteins and their role in signal transduction. The next section focuses on the structural aspects of G proteins, with substantial emphasis on ? subunits. The mechanism of G protein coupling to effector systems is also considered, using the hormone-regulated adenylyl cyclase and light-regulated cGMP phosphodiesterase as models. Subsequent chapters deal with receptors and effector systems, together with the cellular functions that may be regulated by heterotrimeric G proteins. In particular, the interaction of insulin with G proteins is discussed, along with receptor regulation of cell calcium and phospholipase C activity. This monograph should be useful to students and scientists interested in G proteins.