Eukaryotic elongation factor 2 (eEF2) catalyzes translocation and binds to the same site as the aa-tRNA-eEF1A-GTP ternary complex. Given the effects of the mutants on aa-tRNA binding, the effects of seven mutants on eEF2 binding were assayed ( Figure 3E and F, summarized in Table 1 ). For wild-type ribosomes, the dissociation constant for eEF2 was $383 ± 93 nM. Similar values were observed for R232A, K236A and K237A mutant ribosomes, but the R247A mutant promoted an $8-fold increase in affinity for eEF2 (K d $ 47 nM). Among the double mutants assayed, the K237A/K236A mutant promoted the largest increase in affinity for eEF2 ($84 nM, $4.5-fold increase), followed by K236A/R247A ($110 nM, $3.5-fold increase), and K241A/R244A ($229 nM, $1.7-fold increase).