Nucleotide and aminoacyl-tRNA specificity of the mammalian mitochondrial elongation factor EF-Tu.Ts complex

The bovine mitochondrial elongation factor Tu.Ts complex (EF-Tu.Tsmt) promotes the binding of aminoacyl-tRNA to ribosomes. In the presence of GTP, this complex functions catalytically. Both dGTP and ddGTP can replace GTP although about 4-fold higher concentrations are required. ATP, CTP and UTP are not active. ITP can replace GTP when used at 10- to 20-fold higher concentrations. The catalytic use of EF-Tu.Tsmt is inhibited by GDP but not by GMP. XDP also inhibits although about 20-fold higher concentrations are required. EF-Tu.Tsmt will promote the binding of Phe-tRNA to either Escherichia coli or mitochondrial ribosomes. Unlike E. coli EF-Tu, EF-Tu.Tsmt will promote the binding of AcPhe-tRNA to ribosomes about 25% as efficiently as Phe-tRNA. EF-Tu.Tsmt is active in catalyzing the binding of E. coli Met-tRNAmmet to ribosomes. EF-Tu.Tsmt has about 30% as much activity with E. coli Met-tRNAimet but has essentially no activity with E. coli fMet-tRNAimet. Neither yeast Met-tRNAimet nor fMet-tRNAimet is recognized by bovine EF-Tu.Tsmt.