Rab5

Abstract Rab5 has been identified by screening cDNA libraries with degenerate oligonucleotides corresponding to the sequence WDTAGQE shared by members of the Ypt1/Sec4/rab subfamily45. The DNA sequence of canine rab5 (GenBank accession number M35520) predicts a pro tein with a molecular mass of 23,658 Daltons. Canine rab5 protein shows 98% amino acid identity with the human rab5 protein. Like the other members of the rab family, rab5 displays the four highly conserved regions participating in the formation of the GTP-binding site6 and a -CCSN cysteine motif at the (-terminus, which is required for membrane association1 In vitro and in vivo expressed rab5 is post-translationally modified via isoprenylation of the cysteine motif7 and, more specifically, acquires geranylgeranyl groups89. Although isoprenylation is required for membrane association it does not alone specify targeting to specific organelles. The highly variable 34 amino acidlong C-terminal domain of rab5 contains sequences that determine the specificity of localization.