Evidence for a High Affinity, Saturable, Prenylation-dependent p21 Ha-ras Binding Site in Plasma Membranes *

Oncogenic p21 ras proteins can only exert their stimulation of cellular proliferation when plasma membrane-associated. This membrane association has an absolute requirement for post-translational modification with isoprenoids. The mechanism by which isoprenoids participate in the specific association of p21 ras with plasma membranes is the subject of this report. We present in vitro evidence for a plasma membrane binding protein for p21 ras that can recognize the isoprenoid substituent and, therefore, may facilitate the localization of p21 ras.