Language:
  
[Sign in] [Register]   

EIAab logo

Index > News Center > News list.
Enter your KeyWord (Ex. ELISA Kit, Cuticular Active Peptide Factor, etc)
search
Search content in infomation.

    Almost from the time that the genetic code was first deciphered, molecular biologists have tried to determine how the 30S subunit decodes mRNA with such high fidelity. The free energy for a codon- anticodon interaction is only about 2 to 3 kcal mol-1 more favorable for a codon to interact with its cognate anticodon than for that same codon to interact with a near cognate anticodon with just a single nucleotide mismatch. This free energy difference predicts an error rate about 10 - to 100-fold greater than that actually observed. It seemed likely that the ribosome plays some role in stabilizing codon-anticodon interactions. This hypothesis received support from biochemical experiments with bacterial ribosomes that showed N1 methylation of highly conserved adenines at positions 1492 (A1492) and 1493 (A1493) of the 16S rRNA impaired A-site tRNA binding. Similar impairment also was observed when these adenines were changed to guanine or cytosine. Although these experiments indicated that A1492 and A1493 help the ribosome to recognize the shape of the codon-anticodon helix at the A-site, they did not show how they do so.
    Ramakrishnan and coworkers turned to x-ray crystallography to solve the problem. They began by soaking an oligonucleotide containing the tRNAPhe anticodon stem-loop and a U6 hexanucleotide into crystals of the T. thermopbilus 30S ribosomal subunit. The x-ray diffraction data showed that a correct codon-anticodon match causes A 1492 and A1493 to flip out of the loop in which they are normally located and the highly conserved guanine at position 530 (G530) to switch from a syn-to anti conformation. In their new conformations, A1493 and 1492 interact with the first and second base pairs of the codon-anticodon helix, respectively, while G530 interacts with both the second position of the anticodon and the third position of the codon. These conformational changes allow the ribosome to closely......

Polypeptide chain elongation requires three elongation factors

Posted by star on 2019-04-03 01:30:27
Hits:37

Once the translation initiation pathway has established the correct reading frame, the protein synthetic machinery is ready to enter the next stage of protein synthesis, polypeptide chain elongation. A major breakthrough in elucidating the polypeptide elongation pathway came in the mid-1960s when Fritz Lipmann and coworkers showed that three elongation factors isolated from E. coli extracts participate in poly (U)-directed polyphenylalanine synthesis. Subsequent studies by others showed that eukaryotic cells have similar elongation factors. The bacterial elongation factors are named EF1A, EF1B, andEF2, and their eukaryotic counterparts are named eEF1A, eEF1B, and eEF2, respectively. This nomenclature system replaces an older one in which bacterial elongation factors were given names that differed from their eukaryotic counterparts.
EF1A is the most highly expressed protein in E. coli and accounts for about 5% to 10% of total cellular protein. Its intracellular concentration is about 10 times greater than that of ribosomes or EF2. Two nearly identical genes tufA and tufB code for EF1A. Cells require one functional tuf gene to survive. Cells continue to grow if just a single tuf gene is nonfunctional; tufB mutants grow at a normal rate when cultured in rich medium but tufA mutants grow more slowly. The bacterial gene for EF2, fusA, is in the same operon as tufA. The bacterial gene for EF1B, tsf, maps a considerble distance away from the other bacterial elongation factor genes.




Alzheimer's disease is caused by a combination of age, genetics and lifestyle, some of which we can control and others we can't. The best evidence so far suggests that not smoking, drinking only as recommended, maintaining mental and physical activity, eating a balanced diet, and controlling blood pressure and cholesterol levels all contribute to brain health as we age.
A team of British researchers has found that the shorter a woman's fertility window, the higher her risk of developing dementia. They also found that women who had a hysterectomy had a higher risk of developing dementia.
Dr Rosa sancho, head of research at Alzheimer’s research UK, said: 'two-thirds of people with dementia are women and although there are some age differences and women live longer, there may also be a link between estrogen levels and the risk of developing the disease. The onset of menstruation and menopause are important life events for women and it is important to understand how these physiological changes affect brain health. Although the study linked women's reproductive years and hysterectomy to an increased risk of dementia, there is no data on why these factors are relevant. Researchers believe that short-term exposure to estrogen may affect brain health, but so far there has been no experimental proof. The UK's Alzheimer’s research centre is currently conducting a study to further explore why women are more likely to develop dementia than men. The research helps shed light on a complex area of human biology.




Certain small metabolic intermediates influence translation initiation of mRNA molecules by stabilizing or destabilizing the way that a specific region, the riboswitch, in the 5'-untranslated region folds. In the absence of metabolite, the riboswitch folds into a structure that permits the SD in the mRNA to interact with the ASD on the 16S rRNA. In the presence of metabolite (M), the riboswitch folds into a structure in which the SD is part of a helical structure and so cannot interact with the ASD. The remarkable feature of the riboswitch is that specificity for the metabolite is determined entirely by the RNA molecule and does not involve protein; that is, the RNA folds into a structure that binds а sресifiс mеtаbоlitе аnd по оthеrs. Fоr instаnсе, thе ribоswitсh that is part of an mRNA that codes for an enzyme required for thiamine (vitamin B1) synthesis binds thiamine pyrophosphate.
Genes controlled by riboswitches often code for proteins that participate in the formation or transport of the metabolite that is sensed by the riboswitch. Other metabolites that have been shown to regulate translation initiation by their interaction with a riboswitch include vitamin B12, flavin mononucleotide, S-adenosylmethionine, guanine, lysine, and glycine. Riboswitches that influence translation initiation have been demonstrated in bacteria and archaeons. In many cases, the binding of a metabolite to a riboswitch also triggers premature transcription termination because the resultant RNA folding produces a transcription terminator. Plants and fungi also appear to influence splicing rather than translation initiation. In view of the widespread distribution of riboswitches in nature, it would be surprising if riboswitches were not eventually shown to contribute to gene regulation in animals.




Kjeld Marcker and Frederick Sanger discovered the existence of the bacterial initiator tRNA while studying methionyl-tRNA synthetase in1964. They incubated a soluble E. coli extract with [35S] methionine, ATP, and tRNA, expecting to synthesize Met-tRNA. Although they were successful in forming the expected product, they also detected a second product that contained a methionine derivative attached to the tRNA. Chemical analysis revealed the methionine derivative to be N-formylmethionine (fMet). Sanger and coworkers recognized that the formyl group would prevent fMet from being incorporated into a polypeptide chain at any position other than the amino terminus. Subsequent studies showed that bacterial extracts do in fact incorporate fMet into the amino end of a growing polypeptide. Sanger and coworkers showed that bacteria synthesize fMet-tRNA by a two step pathway: (1) methionyl-tRNA synthetase attaches methionine to tRNA to produce methionyl-tRNA and (2) methionyl-tRNA formyltransferase transfers a formyl group form N10-formyltetrahydrofolate to methionyl-tRNA to form fMet- tRNA. Mitochondria and chloroplasts synthesize N-formylmethionyl-tRNA by a similar pathway.
The discovery that bacterial polypeptide synthesis begins with N-fomylmethionine was puzzling because fMet is rarely, if ever, found at the amino terminus of a bacterial protein. The N-formyl group absence was explained when a new enzyme, peptide deformylase, was discovered that cleaves formyl groups from N-termini. Peptide deformylase activity explains why E.coli polypeptides do not have formyl groups at their N-termini but does not explain why the N-terminus is methionine in only about 40% of bacterial polypeptides. The loss of methionine in the other 60% of the polypeptides was explained by the presence of still another enzyme, methionine aminopeptidase, which cleaves the N-terminal methionine from the polypeptides.
Studies performed by Sanger and coworkers......

Page 8 of 117
Hot Genes
ALCAM ACE KSR2 ASPRO C19orf80 Gdf5 Trap1a Atf2
Top Searches
Ubiquitin ELISA Ubiquitin-protein ligase metalloproteinase Asprosin Tumor necrosis TRAP1A vitamin d
Why choose EIAAB
Our products have been quoted by many publications in famous journals such as Cell; Cell Metabolism; Hepatology; Biomaterials.more
Further Information
About us Protein center Bank account Distributors Terms & Conditions Career eiaab.cn

Copyright & copy www.eiaab.com2006-2016 All Rights Reserved    EIAab         Email:eiaab@eiaab.com

Twitter