Expression of intact Ki-ras p21 protein in Escherichia coli.

We have constructed recombinant plasmids capable of expressing in Escherichia coli the intact ras p21 protein encoded by Kirsten murine sarcoma virus. The Ki-ras gene was inserted into an expression vector carrying the E. coli tryptophan promoter and E. coli lipoprotein transcriptional terminator. The resulting plasmids direct the synthesis of large quantities of p21 protein, which represented 20% of the total cellular protein. The Ki-ras p21 protein is immunoprecipitated with monoclonal antibody to p21, and exhibits guanine nucleotide binding activity and autophosphorylation activity. The purified Ki-ras p21 expressed in E. coli has shown to have intact N-terminal and C-terminal amino acid sequences predicted by the nucleotide sequences and migrate as -23K in SDS/polyacrylamide gels.