Figure 3: Proteins containing a C-terminal CAAX box are prenylated by GGTase (if X is Leu) or by FTase. The lipidated proteins are then directed to ER where the RCE1 cleaves the last three amino acids and Icmt methylates the resulting C-terminal cysteine. N-Ras and RhoA are depicted as examples of farnesylated and geranylgeranylated proteins.