Polymerization of an Escherichia coli Elongation Factor Tu

Elongation factor Tu (EF-Tu) from Escherichia coli is shown here to polymerize under conditions of low ionic strength and slightly acidic pH. Several factors, such as decreasing pH, decreasing ionic strength, increasing temperature, and increasing protein concentration (up to 2.5 μM) enhance the rate of polymerization. Both EF-Tu · GTP and EF-Tu · GDP polymerized equally well under the conditions studied. A lag time was observed between the lowering of the pH and the onset of measurable polymerization, which was not overcome by addition of preformed polymer "seeds." Finally, addition of unpolymerized EF-Tu · GDP to a solution of polymerized EF-Tu · GDP appears to lead to formation of new polymers instead of addition to preexisting ones, which may suggest a size limit for polymers of EF-Tu · GDP.