Cloning of two splicing variants of the novel Ras-related GTPase Rab29 which is predominantly expressed in kidney.

cDNA of a novel Ras-related GTP-binding protein was isolated from rat tissue by a PCR-based cloning approach, and was designated Rab29 because its deduced amino acid sequence (204 aa) is remotely similar to that of members of the Rab family (30% identity with Rab1). mRNA of Rab29 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 isolated which contained a 287 bp in-frame insertion with characteristics of an intron sequence; this insertion introduces a stop codon after arginine 167. The recombinant protein (Rab29delta37) derived from the cDNA carrying the insertion was loaded with GTP during biosynthesis, but showed almost no exchange of the nucleotide for radiolabeled GTP. Thus, the C-terminus of Rab29 appears to harbor a structural element which is essential for the nucleotide exchange of the protein.