The Small Gtpase Ran

RAN: AN ATYPICAL GTPASE Mark G. Rush and Peter D'Eustachio New York University School o/Medicine. Department,o/Biochemistry New York NY 10016 ABSTRACT GTPases, proteins that bind and hydrolyze GTP (guanosine triphos phate) are critical regulators of many metabolic pathways. Although these proteins are enzymes that catalyze the hydrolysis of GTP to GDP + Pi, their primary function is not the hydrolysis of GTP per se, but rather the coupling of this hydrolysis to metabolic regulation. Such coupling is gen erally achieved through the interaction of the GTP-bound form of the GTPase with proteins known as effectors. Effectors are often enzymes whose activities are modulated by the GTPase. However, effectors can also be structural proteins involved in assembling intracellular macromo lecular complexes, such as actin filaments and microtubules, as well as proteins involved in the intracellular transport of proteins and RNAs. In deed, the subject of this anthology, the small GTPase Ran, may exert most or all of its regulatory functions by interacting with non-enzyme effectors. This property of Ran distinguishes it from other well studied GTPases, and has resulted in the elucidation of novel mechanisms of Ran action that are quite distinct from previously established paradigms of GTPase function. 1. INTRODUCTION The Ras-related nuclear protein Ran is a highly conserved (80% identity among yeasts and humans) member of the Ras superfamily of small GTP binding and hydrolyzing proteins. Contributors. Preface. Ran: An Atypical GTPase. 1. The Role of Ran in Nuclear Import; M.S. Moore. 2. Ran GTPase Regulation of the CRM1-Dependent Export Pathway; B.M. Paschal, C. Dargemont. 3. Role of Ran GTPase in RNA Processing and Export of RNA from the Nucleus to the Cytosol: Insights from Budding Yeast; A.K. Hopper. 4. Direct and Indirect Roles of RanGTP in Nuclear Export of RNAs in Higher Eukaryotes; E. Lund, J.E. Dahlberg. 5. The Role of Ran in Regulating Microtubule Spindle Assembly; A. Wilde. 6. Multiple Roles of the Ran GTPase During the Cell Cycle; M. Dasso. 7. The Multiple Roles of Ran in the Fission Yeast Schizosaccharomyces pombe; S.S. Salus, S. Sazer. 8. Mitotic Control by Ran and RanBP1 in Mammalian Cells; B. Di Fiore, et al. 9. Ran Regulation by Ran GEF and Ran GAP; F.R. Bischoff, H. Ponstingl. 10. Structural Views of the Ran GTPase Cycle; K. Scheffzek, A. Wittinghofer. Index.