EF-G is a large, five-domain GTPase that promotes the directional movement of mRNA and tRNAs on the ribosome in a GTP-dependent manner. Unlike other GTPases, but by analogy to the myosin motor, EF-G performs its function of powering translocation in the GDP-bound form; that is, in a kinetically stable ribosome-EF-G(GDP) complex formed by GTP hydrolysis on the ribosome. The complex undergoes an extensive structural rearrangement, in particular affecting the small ribosomal subunit, which leads to mRNA-tRNA movement. Domain 4, which extends from the 'body' of the EF-G molecule much like a lever arm, appears to be essential for the structural transition to take place. In a hypothetical model, GTP hydrolysis induces a conformational change in the G domain of EF-G which affects the interactions with neighbouring domains within EF-G. The resulting rearrangement of the domains relative to each other generates conformational strain in the ribosome to which EF-G is fixed. Because of structural features of the tRNA-ribosome complex, this conformational strain results in directional tRNA-mRNA movement. The functional parallels between EF-G and motor proteins suggest that EF-G differs from classical G-proteins in that it functions as a force-generating mechanochemical device rather than a conformational switch. There are other multi-domain GTPases that may function in a similar way.
"The expression of the genes associated with protein regulation of this study (EF1a and EF2) was inhibited significantly at 168 h of exposure to Cu 2+ at the two concentrations used. The elongation factor (EF) is one of the protein families with GTPase activity with two main elongation factors (EF1a and EF2), and there are eukaryote cells with multiple and divergent roles in the cellular metabolism affecting mainly the cytoskeleton, peptide synthesis, and protein degradation (Wintermeyer and Rodnina, 2000). In C. gigas exposed to extended thermal stress the expression of EF was strongly down-regulated in gills after 24 days (Meistertzheim et al., 2007). "
[Show abstract][Hide abstract] ABSTRACT: This study reports molecular markers potentially associated with resistance or sensitivity to the impact of copper in juvenile red abalone, Haliotis rufescens, in the north of Chile under experimental conditions. Genomic analysis was made applying subtractive hybridization libraries (SSH) to identify genes up-and down regulated during cooper exposure in abalone over periods of 12 and 168 h exposed to 2.5 and 10 μg/L of Cu(+2). Results obtained from the SSH library revealed 368 different sequences regulated by copper, that correspond to eight major physiological functions. The validation of these sequences obtained by SSH as well as their expression kinetics were made by PCR in real time on 14 potential genes regulated by metal stress. This study provides information for the characterization of potential genomic markers that may be used in future environmental monitoring and to investigate new mechanisms of stress to copper in this commercially important marine species.
"In contrast to this model, another theory proposes that the binding and release of translocase is not simply bringing the activation energy required to catalyse the translocation . Rather, in coupling the free energy of GTP hydrolysis to translocation, EF-G serves as an authentic motor protein and drives the directional movement of transfer and messenger RNAs on the ribosome (Rodnina et al., 1997; Stark et al., 2000; Wintermeyer and Rodnina, 2000). "
[Show abstract][Hide abstract] ABSTRACT: The lateral flexible stalk of the large ribosomal subunit is made of several interacting proteins anchored to a conserved region of the 28S (26S) rRNA termed the GTPase-associated domain or thiostrepton loop. This structure is demonstrated to adopt puzzling changes of conformation following the different steps of the elongation cycle. Some of these proteins termed the P-proteins in eukaryotes and L10 and L7/L12 in bacteria, present little structural similarities between Eubacteria on one side and Archae and Eukaryotes on the other side. However, up to now, these proteins seem to present a similar macromolecular organisation and they have been involved in the same functions. Convincing evidence attests that these proteins participate in elongation factor binding to the ribosome, and it has been suggested that these proteins might be evolved in a GTP hydrolysis activating protein activity. Involvement of these proteins in the translational mechanism is discussed. Moreover, in eukaryotes, small P-proteins are also found as isolated proteins in a cytoplasmic pool that exchanges with the ribosome-associated P-proteins. Moreover, a part of the ribosomal proteins is phosphorylated (hence their P-protein names). The biological signification of these particularities is discussed.
Biology of the Cell 05/2003; 95(3-4):179-93. DOI:10.1016/S0248-4900(03)00034-0 · 3.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Translocation of the mRNA:tRNA complex through the ribosome is promoted by elongation factor G (EF-G) during the translation cycle. Previous studies established that modification of ribosomal proteins with thiol-specific reagents promotes this event in the absence of EF-G. Here we identify two small subunit interface proteins S12 and S13 that are essential for maintenance of a pretranslocation state. Omission of these proteins using in vitro reconstitution procedures yields ribosomal particles that translate in the absence of enzymatic factors. Conversely, replacement of cysteine residues in these two proteins yields ribosomal particles that are refractive to stimulation with thiol-modifying reagents. These data support a model where S12 and S13 function as control elements for the more ancient rRNA- and tRNA-driven movements of translocation.
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