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At the end of the termination stage in bacteria, the ribosome complex on is still associated with mRNA and a deacylated tRNA, most probably with its acceptor end in the E-site of the 50S subunit and its anticodon end in the P-site of the 30S subunit. During the recycling stage, the ribosomal subunits dissociate from this complex, freeing them to participate in a new round of polypeptide synthesis. In bacteria, this process requires a new translation factor known as the ribosome release factor (RRF).
RRF is an essential protein that was originally thought to bind in the free A-site because its structure is similar to that of tRNA. However, footprinting experiments and cryo-electron microscopy constructs show that instead of binding to the free A-site, RRF binds almost at right angles to this site. EF2•GTP and IF3 somehow assist RRF in disassembling the post termination complex. The details of this disassembly process remain to be determined. Virtually nothing is known about the recycling stage in eukaryotes. Thus far, no eukaryotic counterpart to the bacterial RRF has been discovered. One possibility is that one or more eukaryotic ribosomal proteins assist in recycling SO that a soluble ribosome release factor is not required. Following ribosome disassembly, the small ribosomal subunit is free to interact with the initiation factors to start a new round of polypeptide synthesis.




Cecal cancer is the third leading cause of cancer death in men and women, according to the American cancer society. In a recent study published in the international journal Cancer Research, scientists from Georgia medical university identified a potential new target for immunotherapy for cecal Cancer.
Similar to pd-1, GARP is a special protein expressed on the surface of immune cells in the body, and researchers and colleagues hope to use GARP protein as a new therapeutic approach by targeting it.
The researchers studied how Tregs cells are regulated in a variety of diseases, including tolerance and cancer. Their study of preclinical models found that interfering with GARP can reduce cancer tolerance, inhibit the development of cecal cancer, and inhibit the migration of Treg cells into intestinal tissues.
When researchers study of enteritis mouse model and found that Treg cells on the surface of GARP hereditary eliminate may suppress the immune system to maintain the best tolerated in the bowel way, without GARP, Treg cells can not effectively restrain the body's immune system, in addition, compared to GARP compared to complete mouse model, out on the Treg cells in the cecum cancer mouse model after the GARP, tumors in mice would be halved. In preclinical cancer models, mice without GARP on Treg cells had a good prognosis, and more T cells infiltrated into tumor tissues. Studies have found that this appears to be only in the gut. When the researchers induced cancer in other parts of the mouse body, the presence or absence of GARP on Treg cells did not seem to make a difference.
The researchers found that another cell-surface protein called CD103 may be a signal transduction. When GARP is expressed on the surface of Treg cells, it will grab TGF- secreted by other cells, which will promote the up-regulation of CD103 expression. For Treg cells, this is like the "code" in the gut. In this study, the researchers revealed for the first time the crit......

Bacteria have three protein release factors

Posted by star on 2019-04-09 23:35:12
Hits:20

Polypeptide chain termination takes place when a termination (non-sense) codon enters the A-site on the 30S ribosomal subunit. Early studies suggested that the three bases of the termination codon (UAA, UAG, or UGA) provide all the information required for termination. However, it now appears that bases on either side of the termination codon influence the strength of the stop signal. For instance, UGA is a much stronger stop signal in E. coli when followed by a U than when followed by a C. The next two bases downstream as well as bases just upstream from the termination codon also influence stop signal strength but to a lesser extent.
Polypeptide chain termination in bacteria requires release factors (RFs). The existence of these release factors was first revealed in experiments performed by Mario Capecchi in 1967. He first prepared a ribosome●mRNA complex with a hexapeptide attached to tRNA at the P-site and a termination codon at the A-site and then used this complex to demonstrate that a soluble protein factor was required to release the hexapeptide. C. Thomas Caskey and coworkers devised a much simpler assay for RF activity the following year. Their assay was based on the observation that release factors stimulate an fMet-tRNA●AUG●ribosome complex to release fMet when incubated with a trinucleotide containing a termination codon. Using this simpler assay system, Caskey and coworkers demonstrated that bacterial extracts contain two different RFs. RF1 recognizes the termination codon UAG, whereas RF2 recognizes the termination codon UGA. In addition, both release factors recognize the termination codon UAA. Working independently in 1969, the Capecchi and Caskey laboratories discovered a third bacterial release factor, RF3, which stimulates the rate of peptide release when either RF1 or RF2 is also present but it does not act on its own.

The hybrid-states translocation model offers a mechanism for moving tRNA molecules through the ribosome

Posted by star on 2019-04-09 23:31:15
Hits:12

Once the peptidyl transferase catalyzed reaction is compete, the P-site tRNA is deacylate and the A-site tRNA has a peptide chain with one additional amino acid residue. Before the next elongation cycle can take place, the peptidyl-tRNA has to move from the A-site to the P- site and the deacylate tRNA has to move from the P-site to the E-site so that it can be released from the ribosome. This highly coordinated movement known as translocation has to be precise so that the reading frame of the mRNA is preserved. Although there is general agreement that the ribosome goes through complex changes during translocation, there is little agreement on the nature of these changes.
Noller has proposed the hybrid-states translocation model shown to explain the movements of mRNA and tRNAs through the ribosome. This model is based on chemical footprinting experiments performed by Noller and Danesh Moazed in 1989 that monitored the progress of tRNA through the ribosomes. They first demonstrated that N-acetyl-Phe-tRNA binds to the P-site by verifying its full reactivity with puromycin. Based on this experiment, they assigned the bases protected by N-acetyl-Phe-tRNA in the 16S and 23S rRNA molecules to the 30S and 50S P-sites, respectively. Then they performed a second footprinting experiment after letting the complex react with puromycin. Puromycin did not affect the 16SrRNA footprint but had a profound effect on the 23S rRNA foot-print. The CCAoH end of the now deacylated tRNA moved so that it no longer protected P-site bases on the 23S rRNA but instead protected E-site bases. The tRNA therefore appeared to be in a hybrid state with its anticodon end still bound to the 30S P-site but its CCAoH end bound to 50S E-site.
This hybrid state is represented as P/E, where the letters before and after the slash indicates the 30S and S0S subunit sites, respectively. Movement from the P/P state to the P/E state takes place spontaneously and requires neither......

Exercise can effectively prevent alzheimer disease

Posted by star on 2019-04-09 23:27:33
Hits:14

When we exercise vigorously, our brains release large amounts of feel-good hormones called endorphins. In addition to the feel-good hormones released by exercise, exercise also produces a hormone that boosts memory and helps prevent alzheimer's disease, a new study suggests. The study was led by professor Arancio at Columbia University in the United States
A few years ago, exercise experts discovered a hormone called irisin that is released into the circulatory system during exercise. Initial studies showed that irisin mainly plays a role in energy metabolism. But the new study found that the hormone also promotes the growth of neurons in the hippocampus, an area of the brain important for learning and memory.

Arancio said: "this finding may explain why exercise improves memory and the potential for a protective effect in brain diseases such as alzheimer's."
In the new study, Arancio led an international team of researchers that first looked for a link between irisin and alzheimer's disease in the population. Using tissue samples from brain Banks, they found irisin in the hippocampus, where levels of the hormone are reduced in alzheimer's patients. However, electrophysiological and behavioral analysis showed that the increase of FNDC5/ irisin in the brain of alzheimer's mouse model can significantly improve the plasticity and memory of synapses.
What is the mechanism behind this? The researchers concluded that FNDC5 / irisin reduces the expression of synaptic related genes induced by amyloid beta oligomers and also activates transcriptional inhibition in hippocampal neurons associated with alzheimer's disease.
In these models, irisin also prevents loss of dendritic spines from exposure to amyloid beta oligomers, possibly by reducing the binding of amyloid beta oligomers to neurons and reducing the level of soluble Aβ42. Finally,......

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