The Ha-ras protein, p21, is modified by a derivative of mevalonate and methyl-esterified when expressed in the insect/baculovirus system.

Using the insect/baculovirus expression system, we demonstrate the incorporation of [3H]mevalonate and [3H]methyl groups into recombinant c-Ha-ras protein (p21). Unlike the post-translational palmitoylation of p21 expressed in this system, the modification by mevalonate is not removed by hydroxylamine suggesting the absence of a thioester linkage. It is highly likely that the insect expression system recognizes the C-terminal CAAX Motif in p21, incorporates the mevalonate into the recently described polyisoprenylation modification and carboxyl-methylates the protein.