SHORT COMMUNICATION Human ARHGDIG, a GDP-Dissociation Inhibitor for Rho Proteins: Genomic Structure, Sequence, Expression Analysis, and Mapping to Chromosome 16p13.3 Chaker N. Adra,* ,1 Anand R. Iyengar,* Farzand A. Syed,* Imaduddin N. Kanaan,* Koji Abe, Horacio L. R. Rilo,† Weijiang Yu,* Reshma Kheraj,* Shin R. Lin,* Tadashi Horiuchi,* Samira Khan,* Stanislawa Weremowicz,‡ Bing Lim,* Cynthia C. Morton,‡ and DouglasR. Higgs§ * Harvard Institutes of Medicine, Beth Israel Deaconess Medical Center, and ‡Department of Pathology and Department of Obstetrics, Gynecology and Reproductive Biology, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts 02215; §M RC Molecular Haematology Unit, Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, United Kingdom; and †Section of Transplantation, Department of Surgery, The University of Chicago, Chicago, Illinois 60637 Received May 7, 1998; accepted July 13, 1998 GDP-dissociation inhibitors (GDIs) play a primary role in modulating the activity of GTPases. We re- cently reported the identification of a new GDI for the Rho-related GTPases named RhoGDI. This gene is now designated ARHGDIG by HUGO. Here, in a de- tailed analysis of tissue expression of ARHGDIG, we observe high levels in the entire brain, with regional variations. The mRNA is also present at high levels in kidney and pancreas and at moderate levels in spinal cord, stomach, and pituitary gland. In other tissues examined, the mRNA levels are very low (lung, tra- chea, small intestine, colon, placenta) or undetectable. RT-PCR analysis of total RNA isolated from exocrine pancreas and islets shows that the gene is expressed in both tissues. We also report the genomic structure of ARHGDIG. The gene spans over 4 kb and is organized into six exons and five introns. The upstream region lacks a canonical TATA box and contains several pu- tative binding sites for ubiquitous and tissue-specific factors active in central nervous system development. Using FISH, we have mapped the gene to chromosome band 16p13.3. This band is rich in deletion mutants of genes involved in several human diseases, notably polycystic kidney disease, -thalassemia, tuberous sclerosis, mental retardation, and cancer. The pro- moter structure and the chromosomal location of RhoGDI suggest its importance and underscore the need for further investigation into its biology. © 1998 Academic Press In recent years, the Ras-related superfamily of small GTP-binding proteins has been shown to be involved in a variety of fundamental cellular pro- cesses, including mitosis, intracellular transport, cy- toskeletal rearrangements, and cell morphogenesis (6, 10, 19). An important event central to the bio- chemistry of these small GTP-binding molecules is a cycle of transition from a GTP-bound active state to a GDP-bound inactive state and vice versa (6, 19). This transition is modulated by a group of regulatory proteins that include GDP-dissociation stimulators or GDP-exchange factors, GTPase-activating pro- teins, and GDP-dissociation inhibitors (GDIs) (6, 11). While GDP-dissociation stimulators facilitate the ex- change of bound GDP for GTP, the GDIs prevent release of GDP and thus inhibit activation (6, 11). GTPase-activating proteins catalyze the hydrolysis of GTP to its diphospho derivative and thereby re- verse the activated state of GTPases. Three GDIs specific for the Rho subfamily of pro- teins have been identified (1, 3, 8, 14, 15, 18, 20). The first GDI isolated from bovine brain cytosol, called RhoGDI, is ubiquitously expressed and inhibits the dissociation of GDP from Rho proteins (8, 14). RhoGDI was subsequently found to function also as a GDI for Rac and CDC42. The second member, GDI/ D4, was cloned in our laboratory through subtractive hybridization (1, 15). GDI/D4 is expressed at high levels preferentially in the hematopoietic tissues (15, 18). GDI/D4 could function as a GDI for Rho, Rac, and Cdc42 (1, 18). The mouse homologue of GDI/D4 shows 90% amino acid identity to human GDI/D4 (1). GDI/D4 binds to a spectrum of substrates similar to that of RhoGDI but with a significantly lower affin- ity. Replacement of residues 169 –178 of GDI/D4 with the homologous domain of RhoGDI changes the affinity of GDI/D4 to that of RhoGDI (16). A third Sequence data from this article have been deposited with the GenBank Data Library under Accession No. AF080237. 1 To whom correspondence and reprint requests should be ad- dressed at the Department of Medicine, Division of Hematology/ Oncology, Harvard Institutes of Medicine, HIM 952, 330 Brookline Avenue, Boston, MA 02215. Telephone: (617) 667-3766. Fax: (617) 667-3299. E-mail: cadra@bidmc.harvard.edu. GENOMICS 53, 104 –109 (1998) ARTICLE NO. GE985482 104 0888-7543/98 $25.00 Copyright © 1998 by Academic Press All rights of reproduction in any form reserved.