Abstract

Elongation factor Tu (EF-Tu).GTP has the primary function of promoting the efficient and correct interaction of aminoacyl-tRNA with the ribosome. Very little is known about the elements in EF-Tu involved in this interaction. We describe a mutant form of EF-Tu, isolated in Salmonella typhimurium, that causes a severe defect in the interaction of the ternary complex with the ribosome. The mutation causes the substitution of Val for Gly-280 in domain II of EF-Tu. The in vivo growth and translation phenotypes of strains harboring this mutation are indistinguishable from those of strains in which the same tuf gene is insertionally inactivated. Viable cells are not obtained when the other tuf gene is inactivated, showing that the mutant EF-Tu alone cannot support cell growth. We have confirmed, by partial protein sequencing, that the mutant EF-Tu is present in the cells. In vitro analysis of the natural mixture of wild-type and mutant EF-Tu allows us to identify the major defect of this mutant. Our data shows that the EF-Tu is homogeneous and competent with respect to guanine nucleotide binding and exchange, stimulation of nucleotide exchange by EF-Ts, and ternary complex formation with aminoacyl-tRNA. However various measures of translational efficiency show a significant reduction, which is associated with a defective interaction between the ribosome and the mutant EF-Tu.GTP.aminoacyl-tRNA complex. In addition, the antibiotic kirromycin, which blocks translation by binding EF-Tu on the ribosome, fails to do so with this mutant EF-Tu, although it does form a complex with EF-Tu. Our results suggest that this region of domain II in EF-Tu has an important function and influences the binding of the ternary complex to the codon-programmed ribosome during protein synthesis. Models involving either a direct or an indirect effect of the mutation are discussed.

Highlights

  • The prokaryotic translation factor elongation factor Tu (EF-Tu) mediates the productive interaction of aminoacyltRNA with the ribosome

  • We investigated the functional basis of the lethality of one of these mutations, Gly-280--*Val, which is a mutation at a conserved position in a loop in domain II of Elongation factor Tu (EF-Tu) (Fig. 1)

  • We have presented data showing that a single amino acid substitution in domain II of EF-Tu, Gly280-WVal, abolishes or severely reduces the activity of EF-Tu in translation

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Summary

Introduction

The prokaryotic translation factor elongation factor Tu (EF-Tu) mediates the productive interaction of aminoacyltRNA (aa-tRNA) with the ribosome. We tested whether EF-TuB414 is bound on ribosomes by kirromycin, using translation assays as described above but with a ribosome titration at fixed EF-Tu and kirromycin concentrations (see Materials and Methods).

Results
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