The middle and C-terminal domain (domain II/III) of elongation factor Tu from Thermus thermophilus lacking the GTP/GDP binding domain have been prepared by treating nucleotide-free protein with Staphylococcus aureus V8 protease. The isolated domain II/III of EF-Tu has a compact structure and high resistance against tryptic treatment and thermal denaturation. As demonstrated by circular dichroism spectroscopy, the isolated domain II/III does not contain any α-hellcal structure. Nucleotide exchange factor, EF-Ts, was found to Interact with domain II/III, whereas the binding of amlnoacyl-tRNA, GDP and GTP to this EF-Tu fragment could not be detected.
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