RAS

Ras subfamily of RAS small GTPases
RAS
SMART accession number:SM00173
Description: Similar in fold and function to the bacterial EF-Tu GTPase. p21Ras couples receptor Tyr kinases and G protein receptors to protein kinase cascades
Interpro abstract (IPR003577):

Ras proteins are small GTPases that regulate cell growth, proliferation and differentiation. The different Ras isoforms H-ras, N-ras and K-ras generate distinct signal outputs, despite interacting with a common set of activators and effectors. Ras is activated by guanine nucleotide exchange factors (GEFs) that release GDP and allow GTP binding. Many RasGEFs have been identified. These are sequestered in the cytosol until activation by growth factors triggers recruitment to the plasma membrane or Golgi, where the GEF colocalizes with Ras. Active GTP-bound Ras interacts with several effector proteins: among the best characterised are the Raf kinases, phosphatidylinositol 3-kinase (PI3K), RalGEFs and NORE/MST1.

Ras proteins are synthesized as cytosolic precursors that undergo post-translational processing to be able to associate with cell membranes (PUBMED:12728271). First, protein farnesyl transferase, a cytosolic enzyme, attaches a farnesyl group to the cysteine residue of the CAAX motif. Second, the farnesylated CAAX sequence targets Ras to the cytosolic surface of the ER where an endopeptidase removes the AAX tripeptide. Third, the alpha-carboxyl group on the now carboxy-terminal farnesylcysteine is methylated by isoprenylcysteine carboxyl methyltransferase. Finally, after methylation, Ras proteins take one of two routes to the cell surface, which is dictated by a second targeting signal that is located immediately amino-terminal to the farnesylated cysteine. N-ras and H-ras are expressed stably on the plasma membrane, on Golgi in transfected cells, and at least transiently on the ER. Ras has also been visualized on endosomes.

GO process:small GTPase mediated signal transduction (GO:0007264)
GO component:intracellular (GO:0005622)
GO function:GTP binding (GO:0005525)
Family alignment:
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There are 933 RAS domains in 933 proteins in SMART's nrdb database.

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