Isolation and Characterization of Streptomyces aureofaciens Protein‐Synthesis Elongation Factor Tu in an Aggregated State

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Abstract
The ability of EF-Tu to aggregate spontaneously was employed for the purification of homogeneous EF-Tu · GDP from Streptomyces aureofaciens. The formation of filamentous structures in the aggregated EF-Tu was demonstrated in a light microscope. The purified factor, with a specific activity of 19 100 ± 1000 units/mg in [3H]GDP exchange, was shown to be active in the translation of poly(U). Aggregated EF-Tu · GDP exhibited almost eight-times lower GDP-exchange capacity at 2°C than at 30°C. This suggests that GDP-binding sites are not freely accessible at lower temperatures in the aggregated factor, in contrast to Escherichia coli polymerized EF-Tu. Turbidimetric assays revealed that the solubilization of diluted aggregated S. aureofaciens EF-Tu is strongly dependent on temperature and causes an increase in the number of accessible GDP-binding sites.