CLONING OF 2 SPLICING VARIANTS OF THE NOVEL RAS-RELATED GTPASE RAB29 WHICH IS PREDOMINATELY EXPRESSED IN KIDNEY

cDNA of a novel Res-related GTP-binding protein was isolated from rat tissue by a PCR-based cloning approach, and was designated Rab29 becau se its deduced amino acid sequence (204 aa) is remotely similar to tha t of members of the Rab family (30% identity with Rab 1). mRNA of Rab2 9 was found predominately in kidney. Recombinant Rab29 exhibited rapid exchange of bound guanine nucleotides for radiolabeled GTP but lacked a detectable intrinsic GTPase activity. A second cDNA clone was isola ted which contained a 287 bp in-frame insertion with characteristics o f an intron sequence; this insertion introduces a stop codon after arg inine 167. The recombinant protein (Rab29 Delta 37) derived from the c DNA carrying the insertion was loaded with GTP during biosynthesis, bu t showed almost no exchange of the nucleotide for radiolabeled GTP. Th us, the C-terminus of Rab29 appears to harbor a structural element whi ch is essential fur the nucleotide exchange of the protein.