title: Mutants of the elongation factor EF-Tu, a new class of nonsense suppressors.
abstract: Read-through of nonsense codons has been studied in wild-type Escherichia coli cells and in cells harbouring mutant species of the elongation factor EF-Tu. The two phenomena differ essentially. Readthrough of UGA in wild-type cells is reduced by inactivation of tufB but is restored to the original level by introducing into the cell plasmid-borne EF-Tu. This shows that the natural UGA leakiness is dependent on the intracellular concentration of EF-Tu. Strains of E. coli harbouring mutant species of the elongation factor EF-Tu suppress the nonsense codons UAG, UAA and UGA. Suppression shows a codon context dependence. It requires the combined action of two different EF-Tu species: EF-TuAR(Ala 375----Thr) and EF-TuBo(Gly 222----Asp). Cells harbouring EF-TuAR(Ala 375----Thr) and wild-type EF-TuB, or wild-type EF-TuA and EF-TuBo(Gly 222----Asp) do not display suppressor activity. These data demonstrate that mutated tuf genes form an additional class of nonsense suppressors. The requirement for two different mutant EF-Tu species raises the question whether translation of sense codons also occurs by the combined action of two EF-Tu molecules on the ribosome.
mesh_terms: D001483:Base Sequence; D003062:Codon; D005144:F Factor; D005798:Genes, Bacterial; D005838:Genotype; D009154:Mutation; D010444:Peptide Elongation Factor Tu; D010445:Peptide Elongation Factors / Q000235:genetics*; D013045:Species Specificity; D013489:Suppression, Genetic; D001616:beta-Galactosidase / Q000235:genetics
chemical_list: D003062:Codon; D010445:Peptide Elongation Factors; D001616:beta-Galactosidase; D010444:Peptide Elongation Factor Tu