Bacteria elongation factors

This prevents further ineorporation of aminoaeyl-tRNA by bloeking the binding of EF-Tu GTP. Like the tetraeyelines, fusidie aeid owes its seleetive antimierobial aetion to active uptake by bacteria and exclusion fiom manunalian cells. The equivalent elongation factor in mammalian cells, EF-2 is susceptible to fusidie acid in cell-free systems. 

EFTsNT A UBA-like domain with a clear role outside of ubiquitin binding is found at the N-terminus of EF-Ts proteins. The relationship of this region to genuine UBA domains is well established as there is a structure of full-length EF-Ts available [67]. Nevertheless, this domain is widespread in bacteria and archaea, which obviously lack a proper ubiquitin system. The physiological role of the EFTsNT domain is rather in the binding to the elongation factor EF-Tu, which has no resemblance to ubiquitin. 

The third stage of protein synthesis is elongation. Again, our initial focus is on bacterial cells. Elongation requires (1) the initiation complex described above, (2) aminoacyl-tRNAs, (3) a set of three soluble cytosolic proteins called elongation factors (EF-Tu, EF-Ts, and EF-G in bacteria), and (4) GTP. Cells use three steps to add each amino acid residue, and the steps are repeated as many times as there are residues to be added. 

Other constraints on the temperature at which earlier forms of life lived come from experiments. For example, Gaucher et al.64 compared the sequences of elongation factors from a variety of bacteria to infer the sequences of ancestral elongation factors that may have been present in now-extinct bacteria lying deep in the eubacterial tree. With recombinant-DNA technology, several of those candidate ancestral elongation factors were resurrected for study in the laboratory. They were found to function best at a temperature of about 67°C, typical for modem thermophilic bacteria. 

Despite their antiquity (perhaps 2.5 billion years old), the resurrected ancestral elongation factors are inferred for bacteria that lived long after the origin of life. Nevertheless, the notion that early life lived at high temperatures, in water, and at nearly neutral pH is consistent with available data. For example, a recent reconstruction of the phylogenetic tree of life based on 31 common gene families supports the notion that the last common ancestor lived at high temperatures.65... 

The aaRSs are an ancient family of enzymes that have a lengthy and diverse evolutionary history. For their central role in protein synthesis, the aaRSs generate aminoacylated tRNAs, which are transferred to an elongation factor such as EF-Tu in bacteria for delivery to the ribosome. Some aaRSs have diverged functionally to perform other secondary roles that impact critical cellular activities (4). In addition, paralogs that... 

Sec) (9). In bacteria, Sec is inserted cotranslationaUy at an in-frame UGA codon that is upstream of an RNA stem-loop. In E. coli, SerRS produces the mischarged Ser-tRNA , which is then converted to Sec-tRNA by Sec synthase (SelA). A GTP-dependent elongation factor SelB binds to Sec-tRNA and forms a complex that recognizes specific mRNA sequences called selenocysteine insertion elements (SECIS), that are located 3 to a UGA codon on a stalled ribosome-bound mRNA. It is also responsible for delivering Sec-tRNA to the A site of the ribosome (9). 

GE2270A 394 is an antibiotic produced by Planobispora rosea ATCC 537731. It inhibits Gram-positive bacteria and anaerobes by acting on the protein synthesis elongation factor (EF) <1991JAN693, 1995T4867>. It contains proline, serine, glycine, two thiazolyl amino acids, and a heterocyclic centerpiece of a trisubstituted pyridine, all in a macrocyclic array. 

Bacteria and eucarya are differentially affected by antibiotics that impair ribosome function (and/or fidelity) by directly interacting with, or by perturbing, functionally essential domains of ribosomes and factors. On the basis of their specificity, ribosome-directed and elongation factor-directed antibiotics have been classically subdivided into... 

Unlike the situation in eucarya and bacteria, however, restrictions in ribosome specificity of elongation factors which are similar to, or even more severe than those existing between different domains have been found to exist within the archaea. Three groups, the Methanococcaceae/Thermoplasmales, the Sulfolobales and the Thermoproteales are separated from one another by these restrictions. Thus, ribosomes and factors from different archaea do not freely cooperate in polypeptide synthesis, in striking contrast with the uniform compatibility of ribosomes and elongation factors within each of the two classically recognized domains [182]. 

Each of these sorts of data also supports the deep split within the archaea, into what Woese, Kandler and Wheelis [10] call Euryarchaeota and Crenarchaeota. What the various data sets do not tell us unequivocally is whether, as a monophyletic assemblage, archaea are more recently diverged from eucarya or instead branch with the bacteria. As chapters in this volume reveal, ribosomal protein genes, those for RNA-polymerase subunits and translation elongation factors and some enzymes of metabolism (HMG-CoA reductase, for example [11]) show strong similarity specifically to their eukaryotic homologs, but others exhibit eubacterial affinities, or seem unique. 

One of the primary killers of children prior to immunization was upper respiratory tract infections by Corynebacterium diphtheriae. Toxin produced by a lysogenic phage that is carried by some strains of this bacteria causes the lethal effects. It is lethal in small amounts because it blocks protein synthesis. The viral toxin is composed of two parts. The B portion binds a cell s surface and injects the A portion into the cytosol of cells. The A portion ADP-ribosylates a histidine-derived residue of the elongation factor 2 (EF-2) known as diphthamide. This action completely blocks the ability of EF-2 to translocate the growing polypeptide chain. 

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