No abstract

A recombinant form of the elongation factor 2 from the archaeon Sulfolobus solfataricus (SsEF‐2), carrying the A26G substitution, has been produced and characterized. The amino acid replacement converted the guanine nucleotide binding consensus sequences A‐X‐X‐X‐X‐G‐K‐[T,S] of the elongation factors EF‐G or EF‐2 into the corresponding G‐X‐X‐X‐X‐G‐K‐[T,S] motif which is present in all the other GTP‐binding proteins. The rate of poly(U)‐directed poly(Phe) synthesis and the ribosome‐dependent GTPase activity of A26GSsEF‐2 were decreased compared to SsEF‐2, thus indicating that the A26G replacement partially affected the function of SsEF‐2 during translocation. In contrast, the A26G substitution enhanced the catalytic efficiency of the intrinsic SsEF‐2 GTPase triggered by ethylene glycol [Raimo, G., Masullo, M., Scarano, G., & Bocchini, V. (1997) Biochimie78, 832–837]. Surprisingly, A26GSsEF‐2 was able to hydrolyse GTP even in the absence of ethylene glycol; furthermore, the alcohol increased the affinity for GTP without modifying the catalytic constant of A26GSsEF‐2 GTPase. Compared to SsEF‐2, the affinity of A26GSsEF‐2 for [3H]GDP was significantly reduced. These findings suggest that A26 is a regulator of the biochemical functions of SsEF‐2. The involvement of this alanine residue in the guanine nucleotide‐binding pocket of EF‐2 or EF‐G is discussed.