THE SMALL NUCLEAR GTPASE RAN - HOW MUCH DOES IT RUN

Ran is one of the most abundant and best conserved of the small GTP bi nding and hydrolyzing proteins of eukaryotes. It is located predominan tly in cell nuclei. Ran is a member of the Ras family of GTPases, whic h includes the Ras and Ras-like proteins that regulate cell growth and division, the Rho and Rac proteins that regulate cytoskeletal organiz ation and the Rab proteins that regulate vesicular sorting. Ran differ s most obviously from other members of the Ras family in both its nucl ear localization, and its lack of sites required for posttranslational lipid modification. Ran is, however, similar to other Ras family memb ers in requiring a specific guanine nucleotide exchange factor (GEF) a nd a specific GTPase activating protein (GAP) as stimulators of overal l GTPase activity. In this review, the multiple cellular functions of Ran are evaluated with respect to its known biochemistry and molecular interactions.