Figure 6.

The biogenesis of CAAX proteins requires routing from the ER membrane. Whereas CAAX processing occurs at the ER membrane, CAAX proteins are destined to other membrane sites, for instance the plasma membrane. Transport of CAAX proteins such as Ras from the ER membrane to the plasma membrane could involve trafficking by one of the three possible mechanisms shown: (1) diffusional translocation across the cytoplasm, (2) transport along the cytoplasmic face of known organelles such as those of the secretory pathway, or (3) transport via an as yet unidentified protein, lipid, or vesicular carrier.