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Abstract

The human c−Ha−ras protooncogene product p21C was truncated at the C terminus by 23 amino acids. The resulting G−binding domain, p21 (1−166) = p21C', can be crystallized as a complex with the slowly hydrolyzing GTP analogues guanosin−5'−[beta,gamma−imido]triphosphate, guanosin−5'− [beta,gamma−methylene]triphosphate, and guanosin−5'−O−(3− thiotriphosphate). We show here that this protein has biochemical properties very similar to those of the intact protein. Activating mutations in position 12 (Gly12−−−−Val; Gly12−−−−Arg) have the same effect on the properties of the truncated protein as on intact protein. Nuclear magnetic resonance (NMR) measurements show no apparent effect of the C−terminal deletion on the solution structure of p21. This suggests that neither the structure of the G−binding domain nor any of its biochemical properties are markedly influenced by the truncation