Ha-ras proteins exhibit GTPase activity: point mutations that activate Ha-ras gene products result in decreased GTPase activity.

Abstract

Several ras genes were expressed at high levels in Escherichia coli and the resultant ras proteins were shown to be functional with respect to their well-known specific, high-affinity, GDP/GTP binding. A weak GTPase activity associated with the purified proteins was detected. The normal cellular ras protein (p21N) exhibits .apprxeq. 10 times higher GTPase activity than the activated proteins. Even though the turnover rate of the reaction is very low (0.02 mol of GTP hydrolyzed per mol of p21N protein per minute), the reaction appears to be catalytic; 1 molecule of p21N hydrolyzes > 1 molecule of GTP. The GTPase and the GDP binding activities both were recovered from a MW 23,000 protein eluted following NaDodSO4/polyacrylamide gel electrophoresis, suggesting that these 2 activities are associated with the same protein. Mg2+ ions and dithiotheitol are required for GTPase activity and the optimal pH is between 7 and 8. Guanidine.cntdot.HCl, which is required for solubilizing bacterially expressed ras protein, is strongly inhibitory to GTPase activity at concentrations > 0.5 M.