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Preface Rho-related GTP-binding proteins constitute a functionally distinct group in the small GTPase superfamily. Like Ras, they control intracellular signal transduction pathways, and it is now firmly established that Rhorelated GTPases regulate the organization of the actin cytoskeleton of all eukaryotic cells. Accordingly, this family of GTPases controls cell adhesion, cell movement, and cytokinesis. This volume describes a wide range of experimental approaches that have been used to study the function of Rho-related GTPases both in vitro and in vivo. The availability of recombinant proteins has been of enormous benefit in characterizing the biochemical and biological activities of the GTPases and of the proteins with which they interact. The first part of this volume deals with expression systems used both in Escherichia coli and in insect cells. The driving force for the enormous interest now being taken in the Rho family of GTPases stems from their demonstrated biological roles, particularly as regulators of adhesion and movement. Thus many of the cellular assays that have been used to establish these effects are included in this volume. The ultimate test for any cellular activity attributed to a GTPase is the ability to reconstitute that activity in vitro. To date, this has been achieved only for Rac-dependent activation of phagocytic NADPH oxidase, and several chapters are devoted to this topic. Although the area has already generated an enormous amount of general interest, the functional analysis of small GTPases is still in its infancy. There are many more surprises to come as the biochemical details of the pathways controlled by small GTPases are elucidated. The prize is a molecular explanation of many aspects of contemporary cell biology. We are extremely grateful to all the contributors who have taken the time to commit their expertise to paper, and are confident that their efforts w