INTERCONVERSION OF CRYSTALS OF THE ESCHERICHIA-COLI EF-TU-EF-TS COMPLEX BETWEEN HIGH-DIFFRACTION AND LOW-DIFFRACTION FORMS

Crystals of the complex formed between the two bacterial polypeptide e longation factors, EF-Tu and EF-Ts, produced from solutions of PEG 600 0 can be of two morphologically similar forms both of space group P2(1 )2(1)2(1). One form diffracts to only about 3 Angstrom resolution, the other to better than 2.4 Angstrom resolution. These forms can be inte rconverted and the transformation of one into the other has been shown to be solely a result of dehydration/hydration processes. By designin g a suitable soaking protocol and careful control of the experimental parameters for data collection at cryo-temperatures, complete data set s for the high-resolution form could be obtained.