A role for isoprenoid lipids in the localization and function of an oncoprotein.

Intermediates of the cholesterol biosynthetic pathway are covalently attached to a number of eukaryotic proteins, including the Ras oncoprotein. Ras protein is post-translationally processed at its carboxyl terminus in three steps, resulting in a COOH-terminal cysteine residue to which a polyisoprenoid moiety, probably farnesyl, is attached in a thioether linkage. Polyisoprenylation of Ras protein is required for its membrane association and for the oncogenicity of mutant forms of the protein. Inhibition of polyisoprenylation may offer a route by which Ras-mediated tumors can be pharmacologically suppressed. Other proteins that are polyisoprenylated include nuclear lamin B, fungal mating factors, and subunits of trimeric guanine nucleotide-binding proteins. A consensus sequence for polyisoprenylation (Cys-aliphatic-aliphatic-X) has been identified at the COOH-terminus of modified proteins. Recent evidence indicates that proteins can be modified by several different polyisoprenoids.