Role of domains in Escherichia coli and mammalian mitochondrial elongation factor Ts in the interaction with elongation factor Tu

Bovine mitochondrial elongation factor Ts (EF-Tsmt) stimulates the activity of Escherichia coli elongation factor Tu (EF-Tu). In contrast, E. coli EF-Ts is unable to stimulate mitochondrial EF-Tu. EF-Tsmt forms a tight complex with E. coli EF-Tu governed by an association constant of 8.6 x 10(10). This value is 100-fold stronger than the binding constant for the formation of the E. coli EF-Tu.Ts complex. To test which domain of EF-Tsmt is important for its strong binding with EF-Tu, chimeras were made between E. coli EF-Ts and EF-Tsmt. Replacing the N-terminal domain of E. coli EF-Ts with that of EF-Tsmt increases its binding to E. coli EF-Tu 2-3-fold. Replacing the N-terminal domain of EF-Tsmt with the corresponding region of E. coli EF-Ts decreases its binding to E. coli EF-Tu approximately 4-5-fold. A chimera consisting of the C-terminal half of E. coli EF-Ts and the N-terminal half of EF-Tsmt binds to E. coli EF-Tu as strongly as EF-Tsmt. A chimera in which Subdomain N of the core of EF-Ts is replaced by the corresponding region of EF-Tsmt binds E. coli EF-Tu approximately 25-fold more tightly than E. coli EF-Ts. Thus, the higher strength of the interaction between EF-Tsmt and EF-Tu can be localized primarily to a single subdomain.