The farnesyl group activates Ras toward guanine nucleotide exchange catalyzed by the SOS protein

The farnesyl group and a number of its analogs were enzymatically incorporated into H-Ras and K-Ras in vitro in order to study the prenyl group dependence of the hSOS1-catalyzed nucleotide exchange of Ras. Farnesylation of H-Ras and K-Ras in the absence of further processing was sufficient to facilitate the exchange although fully processed Ras showed a somewhat higher rate of exchange. H-Ras containing 15-carbon analogs of the farnesyl group were good substrates for hSOS1, but geranylated-H-Ras was not.