簡要描述：The mammalian c-H-, c-K- and N-Ras proto-oncogenes encode ubiquitously expressed proteins (1,2). p21Ras can exist in either a physiologically quiescent GDP-binding state or a GTP-binding signal-emitting state (3). Oncogenic p21Ras proteins are trapped in the excited signal-emitting state because the mechanism normally employed to delimit their excitation period, hydrolysis of their bound GTP to GDP, is impaired as a result of specific mutations (3). Interaction of p21Ras with GTPase activating