MUTATIONAL ANALYSIS OF THE ROLES OF RESIDUES IN ESCHERICHIA-COLI ELONGATION-FACTOR TS IN THE INTERACTION WITH ELONGATION-FACTOR TU

The crystal structure of the Escherichia coli elongation factor (EF)-T u.Ts complex indicates that there are extensive contacts between EF-Tu and EF-Ts. To determine the importance of these contacts in the inter action between E. coli EF-Ta and EF-Ts, residues in EF-Ts at the inter face of these two proteins were mutated, The binding constants governi ng the interaction of the resulting EF-Ts variants with E, coti EF-Tu were determined, The effects of these mutations on the ability of EF-T s to stimulate GDP exchange with EF-Tu.GDP and on its ability to stimu late the activity of EF-Tu in polymerization were tested. The results indicate that Arg-12, Met-19, and Met-20 in the N-terminal domain of E F-Ts and His-147 and Lys-166 and/or His-167 in subdomain C of EF-Ts ar e crucial in the interaction between EF-Tu and EF-Ts. Lys-23, Val-234, Met-235, and the C-terminal helix his are less important, The binding constants of the EF-Ts variants governing their interactions with EF- Tu correlate well with their activities in stimulating GDP exchange wi th EF-Tu, Mutations prepared in EF-Tu indicate that His-19 and Gln-114 but not Glu-348 in EF-Tu are moderately important for its interaction with EF-Ts.