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-Ts-mt) stimulates the ac tivity of Escherichia coli elongation factor Tu (EF-Tu), In contrast, E. coli EF-Ts is unable to stimulate mitochondrial EF-Tu. EF-Ts-mt for ms a tight complex with E. coli EF-Tu governed by an association const ant 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-Ts-mt is important for its strong binding with EF-T u, chimeras were made between E. coli EF-Ts and EF-Ts-mt. Replacing th e N-terminal domain of E, coli EF-Ts with that of EF-Ts-mt increases i ts binding to E. coli EF-Tu 2-3-fold, Replacing the N-terminal domain of EF-Ts-mt with the corresponding region of E. coli EF-Ts decreases i ts binding to E, coli EF Tu similar to 4-5-fold, A chimera consisting of the C-terminal half of E. cold EF-Ts and the N-terminal half of EF- Ts-mt binds to E. coli EF-Tu as strongly as EF-Ts-mt. A chimera in whi ch Subdomain N of the core of EF-Ts is replaced by the corresponding r egion of EF-Ts-mt binds E, coli EF-Tu similar to 25-fold more tightly than E. coli EF-Ts, Thus, the higher strength of the interaction betwe en EF-Ts-mt and EF-Tu can be localized primarily to a single subdomain .