Two GTP-driven elongation factors, EF-Tu and EF-G are required to add each new amino acid to the growing polypeptide chain. These factors bind alternately to the the ribosomal GTPase centre located between the 50S and 30S subunits. EF-Tu is responsible for positioning the incoming amino acyl tRNA in the ribosomal "A" site. Once the peptide bond has been formed, EF-G translocates the peptidyl-tRNA from the "A" site to the "P" site (and moves the mRNA through the ribosome) in preparation for the next catalytic cycle.
The region around the GTPase centre includes the sites of action for the castor bean toxin, ricin, and the antibiotics thiostrepton, micrococcin and fusidic acid. Some of these antibiotics are active against common pathogens, including the malaria parasite, Plasmodium falciparum, and the elucidation of the detailed reaction mechanism is therefore of some practical importance.
Detailed ribosomal structures are currently being published, and it is apparent that each translocation step is associated with substantial conformational changes in the ribosome. GTP hydrolysis apparently precedes the "power stroke" when the tRNA is shifted from "A" site to "P" site.
Rapid progress is now being achieved in this area, with numerous papers being published each year. We have therefore provided only the most recent references. It may be necessary to read the earlier papers quoted by these authors in order to fully understand the current position.
It will be difficult for students working on this assignment to quantify the motor activities. Instead you should try to describe the conformational changes on the ribosome which are thought to accompany protein synthesis, and the precise 3-dimensional arrangements of the mRNA and the various tRNAs, insofar as these are presently understood.
Agrawal, RK et al (1999) EF-G-dependent GTP hydrolysis induces translocation accompanied by large conformational changes in the 70S ribosome Nature Structural Biology 6(7), 643-647. [Write down the volume and page numbers for future reference. Click HERE for access instructions. Click HERE to gain access via the Leeds University network.]
Conn, GL et al (1999) Crystal structure of a conserved ribosomal protein-RNA complex
Science 284(5417), 1171-1174. [No electronic version.]
Correll, CC et al (1998) Crystal structure of the ribosomal RNA domain essential for binding elongation factors Proc. Natl. Acad. Sci. USA 95(23), 13436-13441. [Click HERE for the HTML version, or HERE for PDF format.]
Joseph, S & Noller, HF (1998) EF-G-catalyzed translocation of anticodon stem-loop analogs of transfer RNA in the ribosome EMBO J. 17(12), 3478-3483. [Click HERE for the HTML version, or HERE for PDF format. Unfortunately there was a serious mistake in the original article. Click HERE to see the correction in HTML and HERE for the PDF version.]
Justice, MC et al (1999) Mutations in ribosomal protein L10e confer resistance to the fungal-specific eukaryotic elongation factor 2 inhibitor sordarin J. Biol. Chem. 274(8), 4869- 4875. [Click HERE for the HTML version, or HERE for PDF format.]
Porse, BT & Garrett RA (1999) Ribosomal mechanics, antibiotics, and GTP hydrolysis Cell 97(4), 423-426. [No electronic version.]
Porse, BT et al (1999) The antibiotic micrococcin acts on protein L11 at the ribosomal GTPase centre J. Mol. Biol. 287(1), 33-45. [Click HERE for HTML format, or HERE for the PDF version.]
Rodnina et al (1999) Thiostrepton inhibits the turnover but not the GTPase of elongation factor G on the ribosome Proc. Natl. Acad. Sci. USA 96(17), 9586-9590. [Click HERE for the HTML version, or HERE for PDF format.]
Wilson, KS & Noller, HF (1998) Mapping the position of translational elongation factor EF-G in the ribosome by directed hydroxyl radical probing. Cell 92(1), 131-139. [No electronic version.]
Wimberly, BT et al (1999) A detailed view of a ribosomal active site: The structure of the L11-RNA complex Cell, 97(4), 491-502. [No electronic version.]
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If you have comments, queries or suggestions, email me at J.A.Illingworth@leeds.ac.uk