Structure and Function of ras p21: Studies BY Site-Directed Mutagenesis
Are studies by analogy fruitful to understanding protein structure and function? With protein sequences accumulating at an astonishing rate through gene cloning and DNA sequencing, a great deal of protein structure and function can be learned by analogy with members of the superfamily whose structures have been determined and whose molecular mechanisms of action are known. The best case in point, perhaps is in unraveling the elusive function of ras p21. The molecular model of p21 has been constructed by analogy with the crystal structure of the E. coli elongation factor, EF-Tu (McCormick et al., 1985; Jurnak, 1985). This p21 model is remarkably consistent with the actual three dimensional structure of p21 later determined by X-ray crystallography (De Vos et al., 1988). The recent identification of the GAP protein which stimulates GTPase activity of p21 (Trahey and McCormick, 1987), is a conceptual offspring of similar biochemical mechanism well understood for the function of EF-Tu in protein synthesis (Kaziro, 1978). Furthermore, analogy with the well characterized G-proteins, which regulate transmembrane cell signalling in the adenylate cyclase systems and light transduction in retina, forms the foundation for the current belief that ras p21 mediates transmission of growth signals to their intracellular effectors that control cell proliferation and differentiation (Bourne and Sullivan, 1986).
KeywordsGTPase Activity Adenylate Cyclase System Murine Sarcoma Virus Tryptic Peptide Mapping Autokinase Activity
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