Properties of the purified elongation factor 2 in the thermoacidophilic archaebacterium Sulfolobus solfataricus

The elongation factor 2 (aEF-2) has been purified to homogeneity from the extreme thermoacidophilic archaebacterium Sulfolobus solfataricus. It is the only target protein which is ADP-ribosylated by diphtheria toxin in presence of NAD and this modification abolishes its property to support poly(Phe) synthesis in vitro. The factor is constituted by a single polypeptide chain with a relative molecular mass of 78,000 and an isoelectric point of 5.9. aEF-2 is resistant to heat denaturation as shown by the fact that its capability to be ADP-ribosylated was only 10% reduced after 4 h treatment at 80 degrees C. Its amino acid composition does not reveal significant differences with that of analogous factors in other sources; nevertheless, the deviation function indicates that aEF-2 is related to Sulfolobus acidocaldarius and eukaryotes EF-2 more than to eubacterial EF-G or other archaebacterial EF-2.