Crystals of a large tryptic peptide (fragment A) of elongation factor EF‐Tu from Escherichia coli

We have recently described the crystallisation of EF-Tu.GDP from E. coli [ 1 ] and of the product by mild tryptic digestion of this protein [2] polyethylene glycol (PEG) 6000 as a precipitant. crystalline native protein is polymorphic with four trigonal and hexagonal crystal forms. The-tetragonal crystals of the trypsin treated pro- were found to be essentially identical to those described by Sneden et al. [3] and were to contain proteolytically degraded protein. detailed study of the action of trypsin on EF-Tu. by Arai et al. [4] supported our observation [2] mild proteolysis did not destroy the nucleotide properties of the factor even though a number scissions were made in the polypeptide chain. They confirmed the observation made in this laboratory(Wittinghofer and Gast, unpublished results) that by the reaction at 0°C the tryptic digestion of-Tu.GDP could be essentially limited to the produc- of a 39 000 molecular weight species, which they fragment A. We describe here the crystallisation this fragment from polyethylene glycol solutions a form suitable for an X-ray diffraction study.