The ribosomal binding site for eukaryotic elongation factor EF-2 contains 5 S ribosomal RNA

The possible location of RNA in the ribosomal attachment site for the eukaryotic elongation factor EF-2 was analysed. Stable EF-2 X ribosome complexes formed in the presence of the non-hydrolysable GTP analogue GuoPP[CH2]P were cross-linked with the short (4 A between the reactive groups) bifunctional reagent, diepoxybutane. Non-cross-linked EF-2 was removed and the covalent factor-ribosome complex isolated. No interaction between EF-2 and 18 S or 28 S rRNA could be demonstrated. However, density gradient centrifugation of the cross-linked ribosomal complexes showed an increased density (1.25 g/cm3) of the factor, as expected from a covalent complex between EF-2 and a low-molecular-weight RNA species. Treatment of the covalent ribosome-factor complexes with EDTA released approx 50% of the cross-linked EF-2 from the ribosome together with the 5 S rRNA X protein L5 complex. Furthermore, the complex co-migrated with the 5S rRNA X L5 particle in sucrose gradients. Polyacrylamide gel electrophoresis showed that EF-2 was directly linked to 5 S rRNA in the 5 S rRNA X L5 complex, as well as in the complexes isolated by density gradient centrifugation. No traces of 5.8 S rRNA or tRNA could be demonstrated. The data indicate that the ribosomal binding domain for EF-2 contains the 5 S rRNA X protein L5 particle and that EF-2 is located in close proximity to 5 S rRNA within the EF-2 X GuoPP[CH2]P X ribosome complex.