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SV40 T antigen helps to recruit DNA polymerase

Posted by star on 2018-09-04 23:41:38
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    Replication protein A (RPA), a three-subunit SSB complex binds to newly created single-stranded regions, to complete the formation of a proto-replication bubble. RPA prevents single strands from either reassociating or forming intrastrand secondary structures and also interacts with T antigen. RPA and T antigen help to recruit DNA polymerase α-primase, a four-subunit protein complex, to the proto-replication bubble. As the only eukaryotic enzyme that can synthesize primer Pol α is an essential participant in initiation. It is crystal structure has not yet been determined. Pol αhas two distinct catalytic activities, primase and DNA polymerase, which reside in separate subunits.

    The other two subunits appear to play important structural roles but no enzyme activities have as yet been assigned to them. Mammalian Pol α does not have proofreading activity. Primase activity synthesizes RNA oligomers that are 8 to 10 nucleotides long, which serve as primers for DNA synthesis. Then the weakly processive DNA polymerase that is associated with Pol α incorporates 15 to 25 deoxynucleotides before dissociating from the DNA template. Thus, the oligonucleotide synthesized by Pol α consists of an RNA primer joined to a short DNA segment. The first pair of initiator DNA molecules, which are formed on either side of the core origin, serve to prime leading strand formation. Initiator DNA molecules formed by Pol αlater in the replication process prime lagging strand synthesis.



New research suggests that e-cigarette is still harmful to the lung

Posted by star on 2018-09-04 19:10:41
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    E-cigarettes are used as a substitute for traditional cigarettes by many people, but the scientific community is controversial about its health risks. A new study in the UK believes that e-cigarette vapor can damage lung immune cells, and the risk of e-cigarettes may be greater than previously thought.

    In the laboratory, the researchers simulated the exposure of vapors produced by the heating of electronic cigarettes to alveolar macrophages from healthy non-smokers. Alveolar macrophages are immune cells that phagocytose and remove dust, bacteria and allergens. According to Pro-inflammatory effects of e-cigarette vapour condensate on human alveolar macrophages published on Thorax, e-cigarette vapor damages the function of alveolar macrophages. Researchers believe that this suggests that the dangers of e-cigarettes may be greater than previously thought.

    However, the debate surrounding e-cigarettes is still difficult to determine. Previously, British researchers believed that e-cigarettes were less harmful to the body than traditional cigarettes. In addition, the attitudes of the regulatory authorities in different countries are also different. The United Kingdom has approved the sale of some e-cigarette products as cessation aids, but the US has adopted a cautious attitude, especially in the use of e-cigarettes by young people.



The SV40 T antigen binds to the origin and unwinds DNA

Posted by star on 2018-09-03 20:00:31
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    In 1984, Joachim J. Li and Thomas j. Kelly demonstrated that a soluble extract derived from SV40-infected monkey cells could replicate SV40 DNA. Extracts from uninfected monkey cells also supported SV40 DNA replication if they were supplemented with large tumor (T) antigen. Subsequent studies showed that the SV40 T antigen, the only viral protein required for viral DNA replication, acts at the origin of replication (ori) located between the early and late gene regions.

    The T antigen (708 amino acid residues) has four functional domains. Two of these, the origin binding domain and the helicase domain are essential for SV40 DNA replication under in vitro conditions. The obd (residues 131-259) recognizes the viral origin of replication, an essential step for recruiting T antigen to the origin for DNA replication. The helicase domain (residues 265-626) uses energy provided by ATP to unwind DNA. The other two domains, the DnaJ domain (residues 1-82) and the host range (HR) domain (residues 682-708) are not required for in vitro DNA replication. The DnaJ domain, participates in remodeling protein complexes. Xiaojian S.Chen and coworkers have reported crystal structures for the T antigen monomer and homohexamer.

    The sv4o origin of replication contains about 300 bp, but only 64 of these, the so-called core sequence, are essential for DNA replication. Nonessential elements on either side of the core sequence facilitate the initiation process. The core sequence is divided into three functional regions: an early palindrome (EP), a 27-bp region containing the T antigen binding site, and a 17-bp AT-rich region. Two pairs of T antigen molecules bind to four repeated DNA sequences within the core sequence. When ATP is present, each pair of T antigen molecules probably serves as a precursor for the assembly of a double hexamer. The hexamers appear to remain associated with one another throughout the replica......

Eukaryotic DNA Replication Machinery

Posted by star on 2018-09-03 19:52:37
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    Lessons learned from studying bacterial DNA replication also apply to the eukaryotes and archaea. Foremost among these is the semiconservative, semidiscontinuous, and bidirectional nature of DNA replication. Furthermore, eukaryotic and archaeal replication machinery work in much the same way as the bacterial replication machinery for leading and lagging strand synthesis. Even though information gained from bacterial DNA replication studies provides important insights into eukaryotic and archaeal DNA replication, we must also be alert to differences. For instance, the eukaryotic sliding clamp is made of three identical subunits rather than the two that form the prokaryotic clamp. Other differences are of a more fundamental nature. For example, the nuclear replication apparatus in the eukaryotic nucleus must replicate very long linear DNA duplexes.

    Examine the different stages of eukaryotic DNA replication-initiation, elongation, and termination-just as we did for bacterial DNA replication. However, there is no single eukaryotic model system in which all aspects of DNA replication have been studied. Therefore, different eukaryotic systems must be examined to obtain a comprehensive view of the replication process.

    Will focus on two of the best-studied eukaryotic DNA replication systems. The first of these, the Saccharomyces cerevisiae replication system, takes full advantage of yeast genetics to examine DNA replication and is particularly useful for examining the initiation process. The second, the simian virus 40 (SV40) replication system, provides information about the enzymes that participate in DNA chain extension in vitro. Additional eukaryotic systems will be introduced when necessary to consider a fundamental aspect of eukaryotic DNA replication that has not or cannot be studied in the SV40 or yeast model systems.

New findings in inhibiting breast cancer infiltration

Posted by star on 2018-09-03 19:42:53
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    Usually most breast tumors begin in the inner cells of the breast duct, which are surrounded by myoepithelial cells. Previously, scientists believe that the cell layer of myoepithelial cells is a static barrier to prevent cancer infiltration.

    More recently, experiments in laboratory-cultured mouse tissues have shown that the cell layer around the breast duct can reach out and capture escaped cancer cells to prevent their spread in the body. This suggests that the cell layer of myoepithelial cells is an active defense mechanism that inhibits breast cancer metastasis. The paper of Myoepithelial cells are a dynamic barrier to epithelial dissemination was published online in the Journal of Cell Biology.

    It is known that the myoepithelial layer is clinically used to diagnose differential restrictive breast cancer and invasive breast cancer in humans. If breast cancer cells break through the myoepithelial layer, the result is a so-called invasive cancer, which has a higher recurrence rate and requires more aggressive treatment.

    In the study, the researchers engineered cells removed from the inner mammary gland to produce the protein Twist1, which acts by altering gene expression and is involved in cancer metastasis of multiple tumor types.

    Surprisingly, the researchers found that when infiltrating Twist1 cells broke through the myoepithelial layer, myoepithelial cells were able to capture these escaped cells. In a total of 114 observations, 92% of the time it was pulled back into the mammary duct.

    Wuhan EIAab Science Co., Ltd has developed Twist1 kit. Welcome scientific research workers to choose and purchas......

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