Expression Analysis and Chromosomal Assignment of PRA1 and RILP Genes Cecilia Bucci,* ,1 Laura De Gregorio,† and Carmelo B. Bruni‡ *Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Universita ` degli Studi di Lecce, Via Monteroni, 73100 Lecce, Italy; †Division of Experimental Oncology A, Istituto Nazionale Tumori, Via G. Venezian 1, 20133 Milan, Italy; and ‡Dipartimento di Biologia e Patologia Cellulare e Molecolare “L. Califano” and Centro di Endocrinologia ed Oncologia Sperimentale del Consiglio Nazionale delle Ricerche, Universita ` degli Studi di Napoli “Federico II,” Via S. Pansini 5, 80131 Naples, Italy Received August 2, 2001 PRA1 (prenylated Rab acceptor) is a general regula- tor of Rab proteins, while RILP (Rab interacting lyso- somal protein) is a specific effector for Rab7. It has been shown that PRA1 interacts with Rab proteins and with VAMP2. Therefore PRA1 is probably an im- portant factor for membrane traffic, linking together the function of Rab proteins and SNAREs. RILP has a key role in the control of transport to degradative compartments together with Rab7 and probably links Rab7 function to the cytoskeleton. Here we have stud- ied by Northern blot the expression of the two genes in several different human tissues. The 0.8-kb mRNA for human PRA1 is ubiquitously expressed, while the two mRNAs for RILP are differentially expressed. In addi- tion, we have assigned the human PRA1 gene to chro- mosome 19q13.13-q13.2 and the human RILP gene to chromosome 17p13.3. © 2001 Academic Press Key Words: Rab proteins; GTPases; endocytosis; PRA1; RILP; chromosomal mapping. Rab proteins are small GTPases localized to distinct intracellular compartment along the endocytic and exocytic routes and regulate specific steps of vesicular membrane traffic in mammalian cells (1– 4). Several laboratories to understand the molecular mechanism of Rab function have performed extensive search for Rab interacting protein. Using the two-hybrid system, the full-length cDNA coding for prenylated Rab accep- tor (PRA1) has been isolated in rat and human (5, 6). Part of a cDNA highly homologous to rat PRA1 has been cloned previously by the two-hybrid technique using Rab6 as “bait” and named Clone C (7). This represents the mouse homologue. PRA1 seems to be a general regulator of Rab proteins since it interacts with all the Rab proteins tested (5–7). Rab proteins are modified by the geranylgeranyl isoprenoid linked to carboxyl-terminal cysteine residues that allows inser- tion in the membrane (8, 9). PRA1 binds specifically to prenylated Rab proteins since deletion of the C-terminal cysteines abolishes completely the interac- tion (5, 6). Human and rat PRA1 proteins are 94% identical, indicating that PRA1 is very conserved in mammalian cells. Furthermore PRA1 is particularly interesting since it seems to interact preferentially with the activated (GTP-bound) form of Rab proteins and it has been shown to bind to VAMP2 (5, 6), there- fore indicating an important role in connecting Rab and SNAREs function (10 –13). Recently, it has been demonstrated that PRA1 also interacts with Ha-Ras, RhoA, TC21, and Rap1a (14). Therefore, it has been suggested that PRA1 acts as an escort protein for small GTPases by binding to the hydrophobic isoprenoid moi- eties of the small GTPases and facilitates their traf- ficking through the endomembrane system (14). The Rab interacting lysosomal protein (RILP) has been identified as a specific Rab7 effector protein (15). It interacts preferentially with the GTP-bound form of Rab7 and it is important in transport to and mainte- nance of degradative compartments. Indeed, the active form of Rab7 (GTP-bound) is able to recruit RILP on late endosomal/lysosomal membranes. Moreover ex- pression of C-terminal half of RILP, containing the Rab7 binding region, results in inhibition of degrada- tion of different endocytic markers and in the dispersal of lysosomes (15). Similar effects where obtained pre- viously expressing Rab7 dominant negative mutants (16). More interestingly, expression of RILP wt is able to revert the effects of Rab7 dominant negative mu- tants indicating that it could represent a Rab7 effector protein (15). Searches against the Data Bank indicated The GenBank Accession Nos. for human PRA1 and human RILP cDNAs are AJ133534 and AJ404317, respectively. 1 To whom correspondence should be addressed. Fax: +39-0832- 320626. E-mail: cecilia.bucci@unile.it. Biochemical and Biophysical Research Communications 286, 815– 819 (2001) doi:10.1006/bbrc.2001.5466, available online at http://www.idealibrary.com on 815 0006-291X/01 $35.00 Copyright © 2001 by Academic Press All rights of reproduction in any form reserved.