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DNA replication of eukaryotic

Posted by star on 2018-09-11 23:29:19
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    The fact that eukaryotic chromosomes are linear duplexes introduces a problem for eukaryotic DNA replication that does not exist for circular bacterial DNA replication. The ends of eukaryotic chromosomes, termed telomeres, have a G-rich strand that ends in a 3'single stranded overhang.

    Semiconservative replication initiates at origins internal to the telomeric repeats and the replication forks move toward the chromosome ends. Because of the structural arrangement in telomeres, the C-rich strand is always assembled by lagging-strand synthesis and the G-rich strand (denoted by G) is always assembled by leading-strand synthesis.

    Before the structure of the telomere was elucidated, investigators thought that lagging strand synthesis might present a problem because removing the RNA primer at the 5'-end of the last Okazaki fragment would produce a shortened new C-rich strand. However, new C-rich strand synthesis does not necessarily present a problem for the replication machinery because the G-rich stand has a 3'-over-hang. Therefore, the RNA primer at the end of the last Okazaki fragment can be removed without the loss of information.

    In contrast, leading strand replication presents a serious problem because replication of the new G-rich strand will stop at the 5'-end of the C-rich template strand to produce a blunt end with a resulting loss of sequence information. The leading strand problem is thought to be solved by using a 5'→3'exonuclease to generate a 3' over-hang. Unless something is done to restore the lost sequence, this processing step will cause the telomere to become shorter. If this shortening process were to continue through several more replication cycles, then the telomere would be lost entirely and the chromosome would no longer be able to survive as an independent replicating unit. The lead-1ng strand problem is solved by telomerase, a specialized......

SV40 DNA replicated

Posted by star on 2018-09-10 19:46:45
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    Further work in Thomas J. Kelly's and other laboratories led to the identification and characterization of each of the cellular proteins required for SV40 DNA replication. The replication machinery from a large number of different eukaryotes, ranging from yeast to humans has now been studied. These studies show that the components of the replication machinery in the cell nucleus are very similar throughout the eukaryotic domain. Therefore, the discussion that follows describes the eukaryotic elongation stage in general. Our task of studying the eukaryotic replication elongation stage is simplified by the fact that the key eukaryotic proteins that participate during this stage work in the same way as their bacterial counterparts.

    Leading and lagging strand synthesis are coordinate processes in eukaryotic DNA replication just as they are in bacterial DNA replication. For convenience, we will consider the two processes separately. Leading strand synthesis begins after Pol α completes initiator DNA synthesis. A second polymerase, DNA polymerase δ (Pol δ) elongates initiator molecules synthesized by Pol α. The crystal structure for DNA polymerase δ has not yet been determined. Mammalian Pol δ consists of a large subunit that has both 5'→3'DNA polymerase activity and 3'→5'exonuclease activity and a small subunit with a function that has yet to be determined. Pol δ has a low processivity value. However its processivity becomes quite high when it is tethered to DNA by a sliding clamp. Because the eukaryotic sliding clamp was first detected as an antigen in proliferating cells before its function was known, it was called proliferating cell nuclear antigen (PCNA). This name is still used but the more descriptive name of sliding clamp appears to be gaining in popularity. The eukaryotic sliding clamp has a very similar quaternary structure to that described for the bacterial sli......

Effect of AMPK/FIS1-mediated mitochondrial autophagy on LSCs

Posted by star on 2018-09-10 19:33:31
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    Leukemia stem cells (LSCs) are thought to drive the genesis of acute myeloid leukemia (AML) as well as relapse following chemotherapy. Because of their unique biology, developing effective methods to eradicate LSCs has been a significant challenge.

    On June 11, a study published AMPK/FIS1-Mediated Mitophagy Is Required for Self-Renewal of Human AML Stem Cells in cell stem cell showed that Human AML LSCs display high FIS1 expression and unique mitochondrial morphology.

    Human LSC relies on FIS1-mediated mitochondrial autophagy to achieve self-renewal and survival.AMPK is constitutively active in human LSCs, located upstream of FIS1, regulating FIS1 expression, and stimulating mitochondrial autophagy.Destruction of AMPK signaling or FIS1 activity leads to eradication of LSC, which reduces mitochondrial autophagy and impairs the LSC potential of AML. FIS1 loss induces cell differentiation,cell cycle arrest,GSK3 inhibition in AML.

    In AML, mitochondrial translation, mitochondrial DNA copy number, and other properties have been shown to differ from normal hematopoietic cells, suggesting that altering mitochondrial activity plays an important role in leukemia production. In the study, the LSCs of AML are in a unique state of mitochondrial dynamics mediated by AMPK and FIS1 activation, which mediates downstream signaling through GSK3. The data show that AMPK can regulate FIS1 at the gene and protein levels, but it is unclear whether the association between AMKP and FIS1 is direct. AMPK signaling is active in LSCs with low ROS, and inhibition of AMPK leads to loss of LSC potential. It is suggested that AMPK signaling may be a direct node of cell or mitochondrial stress and FIS1-mediated mitochondrial autophagy.

    Wuhan EIAab Science Co., Ltd has developed FIS1 protein, antibody and ELISA kit.

    Welcome scientific research work......

Protein factors are required for DNA initiation in eukaryotes

Posted by star on 2018-09-10 00:55:34
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    The availability of ARS elements, provided the opportunity for investigators to search for protein that interact with the ARS and to examine the steps involved in the initiation of eukaryotic DNA replication. This is a complex and rapidly developing field involving many different proteins. The discussion that follows is limited to the roles of four proteins that are required early in the initiation process, Many of the additional proteins that are required to complete the initiation stage help to regulate replication initiation and to ensure that he origins will fire only once during each cell cycle.

    Stephen P. Bell and Bruce Stillman isolated the first protein, the origin recognition complex (ORC), in 1992 by taking advantage of the fact that ORC · ATP complexes bind to ARS elements. Specifically the ORC · ATP complex protects the A-element and part of the B1 element in ARST from DNase digestion. ORC consists of six different polypeptide subunits. Genes that code for these subunits have been cloned, facilitating genetic and biochemical studies.

    Two lines of evidence suggest that ORC is a reasonable candidate for an eukaryotic initiator. First, yeast mutants with altered ORC subunits have a problem initiating chromosomal DNA synthesis and maintaining ARS plasmids. Second, nucleotide substitutions in the A-element, which reduce binding to ORC in vitro, also lower plasmid stability in vivo. ORC remains bound to yeast ARS throughout the yeast life cycle and helps to recruit three other proteins-Cdc6, Cdt1, and MCM to the ARSs as cells pass from the G1 to the S phase. The order of addition is Cdc6, Cdt1, and then MCM. The functions of these proteins are as follows:

    Cdc6

    Cdc6 is a cell division cycle (CDC) protein. The gene that codes for it, CDC6, was first identified by using a genetic screen designed to identify mutants that i......

New drug therapy restores partial hearing in deaf mice

Posted by star on 2018-09-10 00:44:03
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Deafness is a genetically dominant feature of the LMG2 family, which means that a child inherits a defective copy of the gene from his parents and experiences progressive hearing loss. The mutation of the deafness is located in the region of DFNA27 on chromosome 4. This area contains more than a dozen genes. However, the precise location of this mutation has been unknown.

Most of the previous studies ignored the fourth exon in the Rest gene,because this small exon was not edited into the Rest mRNA of most cells. The normal function of REST proteins is to shut down genes that are only active in a few cell types.

On June 28, a study published Defects in the Alternative Splicing-Dependent Regulation of REST Cause Deafness in Cell showed that exon 4 of mouse Rest was deleted, and ear hair cells died, resulting in a deaf mouse phenotype. The researchers found that many genes that should have been active were shut down before hair cells died. Thus, they reanalyzed the deafness mutations in the LMG2 family and found that the mutations were close to exon 4, altering the boundaries of exon 4, while the REST of hair cells was inactivated.

Integrating exon 4 into REST mRNA is equivalent to a switch that senses hair cells, which shuts down REST and opens up many gene expressions. Activation of these genes is important for hair cell survival and hearing.

Using an exon 4-deficient mouse model, the researchers found that REST inhibits gene expression primarily through a process called histone deacetylation. As a result, they used small molecule drugs that inhibited this process, down-regulating the effects of REST, and successfully restored the mice to partial hearing.

Wuhan EIAab Science Co., Ltd has developed REST protein, antibody and ELISA kit.

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