FIG. 10.

Model of Ras trafficking. After the common processing steps of farnesylation, AAX proteolysis, and methylation which are completed on the cytosolic surface of the ER, the trafficking routes of the different Ras proteins diverge. K-ras, by virtue of its C-terminal polybasic domain, is sorted out of the conventional exocytic pathway and takes an undefined pathway to the cell surface that bypasses the Golgi. H- and N-ras are palmitoylated by an ER-localized palmitoyltransferase and enter the exocytic pathway; they traffic to the cell surface via the Golgi. OMe, carboxymethyl; PalmCoA, palmitoyl coenzyme A; SAM, S-adenosyl methionine; PalmTase, palmitoyltransferase; MethTase, methyltransferase; FPTase, farnesyl protein transferase; Farnesyl-PP, farnesyl pyrophosphate.