The archaeal elongation factor 1 alpha bound to GTP forms a ternary complex with eubacterial and eukaryal aminoacyl-tRNA

The archaeal Sulfolobus solfataricus elongation factor 1 alpha (SsEF-1 alpha) bound to GTP or to its analogue guanyl-5'-yl imido diphosphate [Gpp(NH)p] formed a ternary complex with either Escherichia coli Val-tRNA(Val) or Saccharomyces cerevisiae Phe-tRNA(Phe) as demonstrated by gel-shift and gel-filtration experiments. Evidence of such an interaction also came from the observation that SsEF-1 alpha . Gpp(NH)p was able to display a protective effect against either the spontaneous deacylation or the digestion of aminoacyl-tRNA by RNase A. Protection against the deacylation of aminoacyl-tRNA allowed evaluation of the affinity of SsEF-1 alpha . Gpp(NH)p for both aminoacyl-tRNAs used. The K-d' values of the ternary complex containing S. cerevisiae Phe-tRNA(Phe) or E. coli VaL-tRNA(Val) were 0.3 mu M and 4.4 mu M, respectively. In both cases, the affinity of SsEF-1 alpha . Gpp(NH)p for aminoacyl-tRNA was three orders of magnitude lower than that of the homologous eubacterial ternary complexes, but comparable with the affinity shown by the ternary complex involving eukaryal EF-1 alpha [Negrutskii, B.S. & El'skaya, A.V. (1998) Frog. Nucleic Acids Res. 60, 47-77]. As already observed with eukaryal EF-1 alpha, SsEF-1 alpha in its GDP-bound form was also able to protect the ester bond of aminoacyl-tRNA, even though with a 10-fold lower efficiency compared with SsEF-1 alpha . Gpp(H)p. The overall results indicated that the archaeal elongation factor 1 alpha shares several properties with eukaryal EF-1 alpha but not with eubacterial EF-Tu.