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Composition of bacterial RNA polymerase

Posted by star on 2018-10-09 19:30:24

    Several different groups detected bacterial RNA polymerases at about the same time. Purification and characterization studies revealed that the fully active form of E. coli RNA polymerase, the RNA polymerase holoenzyme, is a large multisubunit protein (molecular mass-459 kDa) that has six subunits. RNA polymerase holoenzymes from other bacteria have the same multisubunit structure and the sequence of each of the subunits appears to have been conserved during evolution.

    RNA polymerase activity is usually assayed using a reaction mixture that contains RNA polymerase (which may be in a crude extract), DNA, Mg 2+ , three nonradioactive NTPs, and one radioactive NTP labeled either in the base with 3H or 14C or in the phosphate attached to the ribose with. 32P. The reaction is stopped by adding trichloroacetic acid which causes the newly formed RNA but not the nucleoside triphosphate precursors to become insoluble, and the precipitate is collected by filtration or centrifugation. The amount of radioactivity in the precipitate is proportional to the amount of RNA synthesized.

    The large size of the bacterial holoenzyme compared to typical enzymes raises the question of whether some complex feature of the polymerization reaction requires such a large enzyme. In fact, E. coli bacteriophage T7 RNA polymerase, which has only one polypeptide subunit with a molecular mass 99 kDa and a tertiary structure (FGi-u T. ) Clearly, the polymerization reaction itself does not require a huge multisubunit bacterial enzyme.

    Clues to understanding reason for the size differences between the E. coli and the T7 phage enzymes come from attempting to use the T7 phage enzyme to transcribe E. coli DNA and studying the gene organization of the T7 phage. First, the T7 phage RNA polymerase can transcribe at best a small fraction of the E. coli genes. Second. T7 phage genes are arranged in only a few ......

Introduction to the bacterial RNA polymerase

Posted by star on 2018-10-09 19:25:44

    RNA polymerase catalyzes nucleoside monophosphate group transfer from a nucleoside triphosphate (NTP) to the 3'-end of the growing RNA chain (or the first nucleoside triphosphate) so that chain growth proceeds in a 5'→3'direction. The essential chemical characteristics of RNA synthesis are as follows:

    1. Phosphodiester bond formation takes place as the result of a nucleophilic attack of the 3'-hydroxyl group on the growing chain (or first nucleoside triphosphate) on the α phosphoryl group of the incoming NTP. This is the same type of reaction that takes place during DNA synthesis. Also, as with DNA synthesis, pyrophosphate hydrolysis drives the reaction to completion.

    2. The DNA template sequence determines the RNA sequence. Each base added to the growing 3'-end of the RNA chain is chosen by its ability to pair with a complementary base in the template strand. Thus, the bases C, T, G, and A in a DNA strand cause G, A, C, and U, respectively, to appear in the newly synthesized RNA molecule.

    3. All four ribonucleoside triphosphates (adenosine 5'-triphos-phate [ATP], guanosine 5'-triphosphate [GTP], cytidine 5'-triphosphate [CTP], and uridine 5'-triphosphate [UTP]) are required for RNA synthesis. When a single nucleotide is omitted RNA synthesis stops at the point where that nucleotide must be added.

    4. The RNA chain grows in the 5'→3'direction that is, nucleotides are added only to the 3'-OH end of the growing chain. This direction of chain growth is the same as that in DNA synthesis.

    5. RNA polymerases, in contrast with DNA polymerases, are able to initiate chain growth so that no primer is needed.

    6. 0nly ribonucleoside 5'-triphosphates participate in RNA synthesis. The first base to be laid down in the initiation event is a triphosphate. Its 3'-OH group is the point of......

Study finds new targets for triple-negative breast cancer treatment

Posted by star on 2018-10-08 18:43:12

    A new study analyzes the transcriptome characteristics of triple-negative breast cancer (TNBC) patients, and identifies and confirms the novel inhibitor Wwox protein of JAK2/STAT3 signaling in breast cancer, elucidating abnormal attenuation of Wwox and abnormal activation of JAK2/STAT3 Such a negative correlation is an important cause of the metastasis of highly malignant TNBC. The study of Loss of Wwox drives metastasis in triple-negative breast cancer by JAK2/STAT3 axis is published online in Nature-Communication.

    In recent years, the incidence of breast cancer in China has continued to rise. TNBC is a type with a high degree of malignancy. Its invasiveness is extremely strong, the risk of distant metastasis is large, and the prognosis is extremely poor. At present, its treatment is relatively simple, mainly chemotherapy, and it is easy to relapse and metastasize. Endocrine therapy and molecular targeted therapy are ineffective against TNBC compared to other types of breast cancer.

    The researchers screened transcriptomic analysis of TNBC cells and normal breast cells to obtain abnormal expression of multiple signals in the IL6/JAK2/STAT3 pathway, demonstrating the high abnormal expression of IL6 in TNBC cells and the persistence of JAK2/STAT3 activation. Activation may be an important factor in the distal metastasis of TNBC. The study also found that SOCS3, the main inhibitor of JAK2/STAT3, was not inhibited in TNBC; the newly discovered fragile site gene Wwox persisted in the IL6/JAK2/STAT3 signaling pathway in breast cancer. Specific inhibition occurs during activation. The researchers demonstrated the inhibitory effect of Wwox on sustained phosphorylation of STAT3 signaling and sustained activa......

Removal of aging glial cells is expected to treat Alzheimer disease

Posted by star on 2018-10-07 23:19:45

    In a new study, aging cells accumulate in their brains before cognitive loss in the mouse model of brain disease. By preventing the accumulation of these aging cells, they are able to reduce tau protein aggregation, neuronal death and memory loss. The relevant research results are published online in Nature, and the title of the paper is "Clearance of senescent glial cells preventing tau-dependent pathology and cognitive decline".

    It is known that senescent cells accumulate in sites associated with aging diseases (including osteoarthritis and atherosclerosis) and neurodegenerative diseases (including Alzheimer's disease and Parkinson's disease) as the natural age grows. In previous studies, we have found that clearing senescent cells from naturally aged mice prolongs their healthy lifespan.

    In this new study, the mouse model of Alzheimer's disease produces sticky, spider-like tau tangles in their neurons, and their genetically modified senescent cells can be eliminated. When senescent cells were removed, the researchers found that the diseased mice maintained the ability to form memory and eliminate signs of inflammation, did not produce neurofibrillary tangles, and maintained normal brain quality. They also reported that drug interventions that remove senescent cells can regulate the accumulation of tau.

    In addition, the research team was able to identify specific cell types that are senescent. When the brain tissue was observed under a microscope, they found two different types of brain cells called microglia and astrocytes to age. These cells are important proponents of neuronal health and signaling, so it makes sense that aging of any of these cells can have a negativ......

How to prevent heart attacks in patients with hypertension

Posted by star on 2018-09-29 19:36:57

    A recent large, long-term study has shown that people with high blood pressure want to prevent heart attacks, while taking antihypertensive drugs and statins (drugs that help regulate cholesterol levels) may be the best option.

    This study was published on The Lancet Journal under the title "Long-term mortality after blood pressure-lowering and lipid-lowering treatment in patients with hypertension in the Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT) Legacy study: 16-year follow-up Results of a randomised factorial trial".

    In the new study, the researchers tracked 8,580 British subjects enrolled between 1998 and 2000, all of whom had high blood pressure.

    According to ASCOT data, hypertensive patients who took amlodipine and perindopril for 5.5 years had a 29% reduction in the likelihood of death from a stroke 10 years later than those who received traditional antihypertensive medication.

    Moreover, compared with patients taking placebo alone, statins were taken at a normal level (6.5 mM per liter) of hypertensive patients, and the risk of death from heart disease and stroke was reduced by 15% after 16 years.

    In addition, patients with “double high” were treated with antihypertensive therapy (amlodipine and perindopril) and conventional cholesterol-lowering therapy, and the likelihood of death from cardiovascular disease was reduced by 21% within 10 years.

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