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    RNA's involvement in polypeptide synthesis, which is taken for granted today, was not firmly established until the 1950s. The earliest clues that RNA plays some role in information flow between genes and polypeptides came from the independent work of Torbjörn Caspersson and Jean Brachet in the late 1930s and early 1940s. Caspersson used cytochemical techniques to show that: (1) most of a eukaryotic cell's DNA and RNA are in its nucleus and cytoplasm, respectively; (2) cells that are actively engaged in protein synthesis have high levels of cytoplasmic RNA; and (3) cytoplasmic RNA tends to be concentrated in small spherical particles. Brachet, using cell fractionation techniques to separate nuclear and cytoplasmic fractions, also observed a correlation between active protein synthesis and high cytoplasmic RNA levels. In addition, Brachet centrifuged the cytoplasmic fraction at high speed to obtain a pellet containing the RNA-rich spherical particles that Caspersson had observed in the cell. Because these RNA-rich particles contained tightly bound proteins, they are more properly described as ribonucleoproteins. By the early 1950s, electron microscopy techniques had improved to the point where they could be used to visualize the spherical ribonucleoprotein particles, which appeared to be about 250 Å in diameter. These particles were known by a variety of different names until 1957, when Richard B. Roberts coined the now universally accepted term ribosome.
    Some eukaryotic ribosomes appear to be free in the cytoplasm, whereas others are attached to the outer surface of a continuous intracellular tubular membrane network that Keith Porter named the endoplasmic reticulum. Regions of the ER that are studded with ribosomes appear rough or grainy in electron micrographs and are therefore known as the rough endoplasmic; reticulum (RER). Regions that lack ribosomes have a smooth appearance and are therefore called the sm......

Chloroplast DNA is also transcribed to form mRNA, rRNA, and tRNA

Posted by star on 2019-03-13 19:20:26
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In green plants, RNA synthesis takes place is a second organelle, the chloroplast, which is the site of all photosynthetic reactions. Each chloroplast has an outer membrane that separates the chloroplast from the cytoplasm and an inner membrane that surrounds a compartment called the stroma. Chloroplast DNA and the chloroplast protein synthetic machinery are present in the stroma.

The stroma also contains flat membranous sacs called thylakoids, which appear to be surrounded by a single continuous membrane that is the site of light-dependent photosynthetic reactions. The Chloroplast is believed to have originated as a cyanobacterial cell that somehow entered a eukaryotic cell. Because the cyanobacterial chromosome codes for more than 3000 different polypeptides and chloroplast DNA codes for only about 75 polypeptides, most protein coding genes were either transferred to nuclear chromosomes or lost during evolution. This transfer or loss probably took place very early in plant evolution because chloroplasts of evolutionarily distant green plants have similar gene content and organization. All chloroplasts arise from pre-existing chloroplasts.

Chloroplast DNA is a circular double-stranded negative supercoil that is about 120 to 180 kbp long. A typical chloroplast many contain as few as ten or as many as a few hundred DNA copies that are organized into nucleoids associated with the inner chloroplast membrane. In addition to their protein coding genes, Chloroplast DNA from higher plants also contain four rRNA genes and 30 tRNA genes. No RNA is imported into chloroplast. Chloroplast genes of higher green plants often contain a single groupⅠor groupⅡintron.

Chloroplast DNA codes for an RNA polymerase that resembles the bacterial core RNA polymerase (α2ββ’)and contains homologous subunits to α, β, and β’. The plastid encoded RNA polymerase(PEP)requires the assistance of a transcription factor that resemb......

The secondary repair mechanism of DNA damage!

Posted by star on 2019-03-13 18:55:03
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    Scientists have confirmed the secondary repair mechanism of DNA damage, demonstrating that cells can sequester damaged DNA through the 53BP1 nuclear bodies and delay replication time to complete the repair.The related research results were published in Nature Cell Biology on 25 February,2019, entitled“53BP1 nuclear bodies enforce replication timing at under-replicated DNA to limit heritable DNA damage”. The research team used fluorescent dyes to label 53BP1-NBs in living cells and tracked them under a microscopes for multiple generations.
    The formation of the 53BP1-NBs interrupts the replication of the DNA chain with the wrong gene, inhibiting DNA replication until the late S phase, leaving valuable time for specific repair.The key molecule of this repair mechanism is a RAD52 enzyme. The enzyme is a tumor suppressor protein that protects DNA from cancer mutations. In addition, this study demonstrates that absence or malfunction of 53BP1-NBs causes premature replication of the affected gene loci.
    The 53BP1-NBs completes the repair of damage in DNA replication, preventing the conversion of stochastic under-replications into genome instability,and slowing the spread of DNA damage in cells. In addition, the study showed that 53BP1-NBs completed gene repair after mitosis, revealing for the first time the possibility that whole genome replication may need to exceed one cell division cycle.
    This finding may play an important role in improving cancer treatment. Many anticancer drugs destroy the DNA of rapidly dividing cancer cells, so understanding the timing and mechanisms of DNA repair is critical to the development of new drugs and minimizing the side effects of current treatments.
    Wuhan EIAab Science Co., Ltd has developed RAD52 protein,antibody and ELISA kit.Welcome scientific research workers to choose and purchase.


UROMODULIN

Posted by star on 2019-03-11 20:04:22
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    Uromodulin or Tamm-Horsfall protein (THP) is a 90-KDa protein of high glycosylation almost exclusively in the kidney by the epithelial cells lining the thick ascending limb (TAT) of the loop of Henle and early distal tubules. It is the most abundant protein in healthy human urine.
    The domain composition of uromodulin includes a leader peptide directing its entry in the secretory pathway, three epidermal growth factor (EGF)-like domains (EGF-Ⅱ and EGF-Ⅲ predicted to be calcium binding), a central domain of unknown function, a zona pellucida (ZP) domain, and a glycosylphosphatidylinositol-anchoring site.
    Uromodulin may contribute to colloid osmotic pressure, retards passage of positively charged electrolytes, prevents formation of supersaturated salts and their crystals. Uromodulin gene knockout mice exhibit progressive renal papillary calcification and formation of calcium oxalate stones.
    Uromodulin can defense against a urinary tract infection. When uromodulin production is increased , it is likely that the kidney is counteracting uncontrolled systemic inflammation through inhibiton of cytokine/chemokine signaling or via activation and polarization of macrophages. Studies in mice demonstrated that uromodulin binds to and inhibits the type 1 fimbriae of Escherichia coli.
    Uromodulin is also critical for modulating renal ion channel activity, salt/water balance, rental and intertubular communication.
    More recent findings that polymorphisms in uromodulin gene are strongly associated with chronic kidney disease, Mutations in uromodulin gene cause familial juvenile hyperuricemic nephropathy, medullary cystic kidney disease type 2 that autosomal dominant tubulointerstitial kidney disease.
    Lower levels of serum uromodulin may identify early kidney function loss even when serum creatinine values are still within......


    Once the pre-initiation complex is assembled at the promoter, the players are in position to begin transcription elongation. The RNA polymerase Ⅲ transcription machinery melts the DNA flanking the transcription initiation site. TFIIIB is an active participant in this melting event. The first two nucleotides line up on the now exposed template strand and transcription elongation begins. Almost all of the RNA polymerase Ⅲ molecules escape from the promoter without significant pausing or arrest. Once a crystal structure becomes available for RNA polymerase Ⅲ,it will be interesting to compare it with that of RNA polymerase Ⅱ to see if there are obvious structure difference that explain why the two polymerase differ in their abilities to escape the promoter.
    The RNA polymerase Ⅲ transcription elongation complex moves at about the same rate as the RNA polymerase Ⅱ transcription elongation complex but, unlike the RNA polymerase Ⅱ transcription elongation complex, does not appear to appear to require any dedicated factors for transcription elongation. However, a subunit that is unique to RNA polymerase Ⅲ has significant homology to the elongation factor SII. Perhaps this polymerase subunit eliminates the need for SII.
    The bound transcription initiation factors might be expected to block transcription elongation through transcription units with type 1 or 2 promoters. However, this blocking does not seem to occur. Moreover, multiple passages of RNA polymerase through a transcription unit do not remove the assembled transcription initiation factors from the transcription unit. One possibility is that RNA polymerase Ⅲ transiently displace one transcription factor as it moves through the transcription unit but protein- protein interactions with other transcription initiation factors permit the displaced factor to remain associated with the promoter.
    RNA polymerase Ⅲ can efficiently term......

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