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. 2011 Mar;2(3):275–287. doi: 10.1177/1947601911407329

Figure 5.

Figure 5.

Ral posttranslational processing. Ral is synthesized initially as an inactive cytosolic protein. The cytoplasmic (GGTase-I)– or endoplasmic reticulum (Rce1 and ICMT)–associated enzymes recognize the Ral C-terminal CAAX motif, leading to covalent addition of a geranylgeranyl isoprenoid to the cysteine residue of the CAAX motif, followed by proteolytic cleavage of the AAX residues and carboxylmethylation of the now terminal prenylated cysteine. Sequences upstream of the CAAX motif are rich in K or R basic amino acids. These polybasic stretches comprise a second membrane-targeting signal. Reversible phosphorylation of S194 in RalA modulates the targeting activity of the C-terminus, altering subcellular location. CAAL = cysteine–aliphatic amino acid–aliphatic amino acid–leucine; the terminal amino acid of the CAAX tetrapeptide motif dictates prenyltransferase specificity, with leucine recognized by geranylgeranyltransferase-I (GGTase-I); K/R = basic amino acid–rich sequences; Aur-A = Aurora A; GGTI = GGTase-I inhibitor; PKI = protein kinase inhibitor; Rce1 = Ras-converting enzyme 1; Icmt = isoprenylcysteine carboxyl methyltransferase.