Membrane association appears to be an essential step for transformation by ras proteins; mutated ras proteins which are cytosolic fail to cause transformation. Ras undergoes a series of carboxy terminal modifications which generate the membrane-bound form of protein. Attachment of the fatty acid palmitate was the first C-terminal modification identified, and was presumed to be the major reason that ras associated with membranes. Three additional processing steps have been discovered very recently--removal of the final 3 C-terminal residues, methylation of the newly exposed alpha- carboxyl group, and the quite unusual attachment of an isoprenoid moiety. These modifications, particularly the addition of the C15 (farnesyl) hydrocarbon, have the potential to participate in membrane association of ras. The discovery of these new modifications of ras necessitates a re- evaluation of our ideas about how rats binds to membranes. This application proposes to examine carboxy terminal modifications, with an emphasis on farnesylation, to determine each steps' contribution to membrane binding. The goal is to understand how ras interacts with membranes with the aim of developing means to disrupt this interaction as novel methods to inhibit transformation, not by controlling enzymatic activity, but by spatially regulating access of ras to proteins which trigger or transmit its oncogenic signal. The contribution of farnesylation to membrane binding and transformation will be examined in two ways: by constructing mutant ras genes encoding proteins in which modification is interrupted at each step of the pathway; and by examining the growth of ras-transformed cells in which farnesylation has been inhibited. These studies should provide a clearer understanding of how membrane binding controls ras transforming activity.
