Rab-family GTPases function as key regulators for membrane traffic. Among them, Rab45/RASEF is an atypical GTPase in that it contains a coiled-coil motif at the mid region and a distinct N-terminal EF-hand domain with C-terminal Rab-homology domain. Here, we provide the initial biochemical characterization and intracellular localization of human Rab45. Rab45 bound guanine nucleotide tri- and di-phosphates through the C-terminal Rab domain. Rab45 was capable of self-interacting, and the self-interaction required the mid region containing the coiled-coil motif. Rab45 expressed in HeLa cells was localized in a small patch in the perinuclear area of the cell, and the localization was regulated by the guanine nucleotide-bound states of Rab45. Interestingly, the mid region, together with Rab domain, appeared to be essential for the characteristic perinuclear localization of Rab45, indicating that the self-interaction may be involved in the intracellular localization of Rab45. (c) 2007 Elsevier Inc. All rights reserved.