Characterization of ras Proteins Produced at High Levels in the Baculovirus Expression System
The p21 protein products of Ras oncogenes have been produced in a variety of expression systems. Most workers have used bacterial systems, which although producing good yields have several drawbacks. The recombinant bacterial p21 has frequently been produced as an insoluble prptein requiring the presence of strong denaturants during purification1,2 or as a fusion protein3–5. Even when soluble it most likely retains the N-terminal methionine6 (or formyl-methionine residue) and always lacks the post-translational addition of palimitic acid which is essential for its biological activity and its translocation to the membrane7,8. Furthermore, soluble E.coli expressed p21 protein can be heterogeneous due to C-terminal proteolysis and possibly incorrect protein-folding. For example, we observe that recombinant-N-ras p21 can elute as several peaks on ion exchange chromatography and can Chromatograph anomolously during gel filtration. Palmitoylated p21 has been produced in several eukaryotic cell lines but generally at much lower levels9,10.
KeywordsBACULOVIRUS Expression System Baculovirus System Polyhedrin Promoter Murine Sarcoma Virus Strong Denaturant
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