ABSTRACT
We characterized the normal (Gly-12) and two mutant (Asp-12 and Val-12) forms of human N-ras proteins produced by Escherichia coli. No significant differences were found between normal and mutant p21 proteins in their affinities for GTP or GDP. Examination of GTPase activities revealed significant differences between the mutant p21s: the Val-12 mutant retained 12% of wild-type GTPase activity, whereas the Asp-12 mutant retained 43%. Both mutant proteins, however, were equally potent in causing morphological transformation and increased cell motility after their microinjection into quiescent NIH 3T3 cells. This lack of correlation between transforming potency and GTPase activity or guanine nucleotide binding suggests that position 12 mutations affect other aspects of p21 function.
Subject(s)
Cell Transformation, Neoplastic , Oncogenes , Proto-Oncogene Proteins/genetics , Animals , Cells, Cultured , Escherichia coli/genetics , GTP Phosphohydrolases/metabolism , Guanosine Diphosphate/metabolism , Guanosine Triphosphate/metabolism , Humans , Mice , Mutation , Protein Binding , Proto-Oncogene Proteins/metabolism , Proto-Oncogene Proteins p21(ras)ABSTRACT
Fibroblasts transformed by ras oncogenes display enhanced cell surface ruffling and fluid-phase pinocytotic activities. Microinjection of antibodies that specifically bind the ras proteins into these cells results in the inhibition of these two surface activities. The possible underlying biochemical basis of the influence of the ras proteins on membrane ruffling and pinocytosis and the potential relationship of these two biological activities to membrane signal transduction are discussed.
