title: Isoprenylation of the low molecular mass GTP-binding proteins rac 1 and rac 2: possible role in membrane localization.
abstract: Ras proteins can be modified at their COOH-terminal cysteine in the motif Cys-Ali-Ali-Xaa by a farnesyl isoprenoid. This modification is essential for membrane association and biological activity of ras proteins. A similar COOH-terminal amino acid sequence, Cys-Xaa-Ali-Xaa, exists in the ras-related GTP-binding proteins rac 1 and rac 2. To determine whether these proteins were similarly modified, COS cells were transfected with rac 1 and rac 2 cDNA and expressed proteins were labeled with [3H]mevalonic acid. We report here that both rac 1 and rac 2 are post-translationally modified by addition of an isoprenoid group, the likely site of which is the COOH-terminal cysteine. Isoprenylation was found only in racs associated with particulate cell fractions, suggesting that this modification may be associated with membrane localization of the proteins. These data specifically identify mammalian low molecular mass GTP-binding proteins other than ras that undergo post-translational modification and further define the COOH-terminal consensus sequence, Cys-Ali-Ali-Xaa, as an isoprenylation signal. This sequence may identify a larger family of low molecular mass GTP-binding proteins which are isoprenylated.
authors.affiliation: Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710.
authors.forename: J R
authors.initials: JR
authors.lastname: Didsbury
authors.forename: R J
authors.initials: RJ
authors.lastname: Uhing
authors.forename: R
authors.initials: R
authors.lastname: Snyderman
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D008798:Mevalonic Acid / Q000378:metabolism*; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000138:chemical synthesis; D015689:Oncogene Protein p21(ras) / Q000235:genetics; D011499:Protein Processing, Post-Translational; D012689:Sequence Homology, Nucleic Acid; D013347:Subcellular Fractions / Q000378:metabolism; D014162:Transfection; D020744:rac GTP-Binding Proteins
chemical_list: D000906:Antibodies; D009842:Oligopeptides; D019204:GTP-Binding Proteins; D015689:Oncogene Protein p21(ras); D020744:rac GTP-Binding Proteins; D008798:Mevalonic Acid