Molecular Properties of Two Mutant Species of the Elongation Factor Tu
Journal Article
Overview
abstract
The molecular properties of two mutant species of the elongation factor Tu (EF‐Tu), derived from either tuf A or tufB, have been studied. One, designated EF‐TuAR, is the product of a kirromycin‐resistant tufA gene. The other designated EF‐TuBo is a tufB product and is present in a kirromycin‐resistant mutant of Escherichia coli (LBE 2012) also harbouring the EF‐TuAR species. EF‐TuAR has been isolated in homogeneous form as a single gene product from the mutant strain LBE 2045, in which the tufB gene has been inactivated by an insertion of the bacteriophage Mu. EF‐TuBo has been isolated from LBE 2012 together with EF‐TuAR in a 1:1 mixture. Fractionation of this mixture on DEAF‐Sephadex A‐50 resulted in an enrichment of EF‐TuBo of about 80%. The properties of EF‐TuAR and EF‐TuBo have been compared to those of a kirromycin‐sensitive species designated EF‐TuAS, which was isolated from LBE2045 by transduction of wild‐type tufA.We show here that all three EF‐Tu species are fully competent to sustain polypeptide synthesis. All also appear to interact normally with guanine nucleotides and EF‐Ts. Only in the presence of the antibiotic do the following differences appear. (a) Kirromycin causes EF‐TuAS (wild‐type tufA gene product) to be retained on, and thus block, the ribosome. (b) EF‐TuAR fails to bind the antibiotic and thus is capable of protein synthesis in its presence. (c) EFTuBo fails to sustain polypeptide synthesis upon binding of kirromycin. It does not, however, block the ribosome, so the strain harbouring both this protein and EF‐TuAR (LBE2012) is kirromycin resistant.
