Interactions of elongation factor EF-P with the Escherichia coli ribosome

In all cells, ribosomes are inert in the absence of several proteins that promote each facet of protein synthesis. In eubacteria, initiation factors (IF-1, IF-2, IF-3) bind to the 30S subunit, whereas elongation factors (EF-Tu and EF-G) and termination factors (RF-1, RF-2 and RF-3) bind to 70S ribosomes. Reconstitution of synthesis using all of these homoge-neous proteins revealed that they are insufficient for synthesis directed by a native mRNA and that several other proteins are required [1–6]. One of these pro-teins, EF-P, stimulates peptide bond synthesis by 70S ribosomes [1,2,6–8]. The gene encoding EF-P, efp, occurs at a unique site at 94.3 min on the Esc-herichia coli chromosome [9]. Interruption of the efp gene is lethal to the cell and results in an abrupt cessation of protein synthesis, specifically in an impairment of peptide-bond formation [10]. Cells deleted for efp grow only in the presence of the efp gene in trans. Thus, the efp gene is essential for cell growth and viability [10,11]. Reconstitution experiments and the effect of various antibiotics suggest that EF-P binds to a site on ribo-somes that differs from the binding site of most other translation factors. Thus, EF-P requires ribosomal pro-tein L16 for its action, but not L7 ⁄L12, L6 or L11 [12]. All of the G proteins, IF-2, EF-Tu, EF-G and RF-3 act with L7 ⁄L12 in the sarcin-ricin loop to trig-ger GTP hydrolysis, and L6 is required for the action of the release factors [6]. Several antibiotics perturb the action of EF-P. Notably, streptomycin, which impairs translational fidelity, is a strong inhibitor of the EF-P reaction [12]. However, other antibiotics that alter the fidelity of decoding such as neomycin and kasugamycin, have no effect on the EF-P-mediate