Cross-linking of tRNA at two different sites of the elongation factor Tu

Recently, we reported on the induction by kirromycin of two tRNA binding sites on elongation factor Tu. To obtain independent information on the existence of these two sites and to characterize them further, 3' oxidized tRNA was cross-linked to elongation factor Tu by [3H]borohydride reduction. Specific cross-linking occurred exclusively in the presence of kirromycin. In the case of elongation factor Tu X GDP X kirromycin, cross-linking was found at lysine-208; in elongation factor Tu X GTP X kirromycin, cross-linking was at lysine-208 and lysine-237. In both elongation factor Tu complexes, kirromycin itself was found cross-linked to lysine-357. The tRNA cross-linking sites are in agreement with the idea of two different binding sites of tRNA on elongation factor Tu.