The transcription process of RNA.

RNA synthesisthree stages of identification and starting, prolonging and terminating.(i) Identification oftranscription begins at a specific part of the
DNA
molecule, which is also the part of the RNA polymerase-whole enzyme binding that is the initiators. Why can RNA polymerases bind only at the initiators? Obviously, the nucleotide sequence at the initiation is special, in order to facilitate, people will start transcription on the DNA of the first base is set as 1, along the direction of transcription down the nucleotide sequence are expressed in positive values;comparing the sequences of more than 100 pro initiators of the original nucleus,found that there were two conservative sequences upstream at about -10bp and -35bp upstream of the RNA transcription starting point, and a set of 5'-TATAATpu sequences near -10bp, which Pribnow first discovered called Pribnow boxes, where RNA polymerases bind to each other.
-35bp, there is a sequence of 5'-TTGACG δ-; The importance of the -35 sequence also depends on the strength of the starter to a large extent.because RNA polymerase molecules are large and can cover about 70bp of DNA sequences, a suitable part of the enzyme molecule can occupy a sequence area from -35 to -10.the initiators of nuclear organisms have their own particularity, the nuclear organisms have three kinds of RNA polymerase, each of which has its own type of initiators. Taking the startup structure of RNA polymerase II. as an example, people compared hundreds of celebrinate nucleotide sequences of celebrinates of celebrinates of celebrinates in the ceretics of the ceretics of the nuclease II; in the -25 region, there are TATA boxes, also known as Hogness boxes or Goldberg-Hogness boxes.
its consistent sequence is T28A97A93A85A63T37A83A50T37, basically composed of A, T base, ionoid transcription experiments show that the TATA box determines the choice of transcription starting point, the natural lack of TATA box can start transcription from more than one site. There is a CAAT box in the -75 zone, and its consistent sequence is GGTCAATCT. Experiments have shown that CAAT boxes are related to transcription starting frequency, e.g. missing GG, and the β globulin gene transcription efficiency of rabbits is only 12% original.In addition to the promoter, there is a sequence called enhancer upstream of the initiation point of the uterine transcription, which greatly enhances the activity of the promoter, its position is often not fixed, can exist upstream or downstream of the promoter, for the promoter they are positive and reverse arrangement are valid.
also enhances heterogeneity genes, but many experiments have confirmed that it may still be tissue-specific, such as the
immunoglobulin
gene enhancer only in B lymphocyte activity is the highest, insulin gene and pancreatic lactase gene growth also have a high tissue specificity.(ii) Transcription Start and ExtensionIn primary nuclear organisms, when the δ sub-base of the RNA polymerase discovers its identification site, the whole enzyme binds to the sequence of -35 regions of the initiators to form a closed starter complex. Due to the large size of the whole enzyme molecule, the other end of it can be in the sequence to -10 region, under some action, the whole enzyme molecule to -10 sequence transfer and firmly bind with it, where the local DNA 12-17r dechain formation of the whole enzyme and the open compound of the promoter.
the starting and extending bits in the open starter complex are filled with corresponding nucleotide presupers, forming the first phosphate bonds of RNA under the catalysis of the RNA polymerase β subbase.the first nucleotide synthesized by
RNA always has GTP or ATP, which is common in GTP, where the δ factor is dissophed from the whole enzyme, sliding downstream by the core enzyme on the DNA chain, and the falling δ factor binds to another core enzyme to form the whole enzyme for reuse.The start of transcription of urns is complex and often requires the assistance of multiple protein factors, and it has been known that there is a class of
protein
molecules called transcription factors in all cells that form transcription start complexes with RNA polymerase II. the endogenetic biogenetic gene, there are genes specifically encoded for proteins, which are the responsibility of RNA polymerase II. According to the function characteristics of these transcription factors can be broadly divided into two categories, the first category is universal transcription factors they and RNA polymerase II. together to form a transcription starting complex, transcription can start at the right place.
common transcription factors are made up of a variety of protein molecules, including proteins specific to the TATA box, called TATA box binding proteins, and a group of complexes called transcription factor II.D. TFII.D is then combined with RNA polymerase II. In addition to TFII.D, TFII.A, TFII.F, TFII.E, TFII.H, etc. are also found in the nuclease extract, which play a role in different stages of assembly of transcription starting compounds, such as TFII.H, which has rotary enzyme activity, which can use the energy generated by ATP decomposition to mediate the opening of the starting point double helix, so that polymer RNA enzymes can function.
It is not difficult to see from this that the beginning of gene transcription in the nucleocytes is the key to gene expression regulation, so many protein molecules interactions, and these protein molecular DNA regulation without a piece of the combination, forming a complex system to control the beginning of gene transcription. The second type of transcription factor is a tissue cell-specific transcription factor, or inducable transcription factor, which is a class of transcription factors that are required when specific tissue cells or after being stimulated by some steroid
hormone
,
growth factor
or other stimuli. such as the activator protein-1 is a class of induced transcription factors, it is composed of a multi-protein composition of the complex, can be produced by the fos gene and jun gene family protein products.
When certain growth factors
cellular factors
and certain chemicals stimulate these cells outside the cell, the intracellular JUN protein and FOS protein phosphate, specifically binding to the c-jun gene and c-fos gene promoter site, so that these genes are trinated and translated the corresponding c-JUN protein and c-FOS protein, these proteins can form a djumer AP-1, AP-1 will bind to the cell nucleus of the target gene regulation site, promote or activate the transcriptional activity of the target gene, resulting in the specific reaction of these cells due to extracellular stimuli, the expression of the specific protein molecules. For more information, see the chapter on signal transcription. . The extension of the RNA chain is catalyzed by the core enzyme, which reacts with the DNA template on the first GTP RNA 3'-OH on the starting complex to form a phosphate phosphate deester bond. The polymerized nucleotides and UC 3'-OH are free, so that they can be extended one by one according to the guidelines of the template DNA. So the synthesis aspect of the RNA chain is also 5'--3.
because the DNA strand has an anti-parallel relationship with the synthetic RNA chain, the RNA polymerase moves along the DNA strand 3'-5'. The entire transcription process is a continuous break-down reaction by the same RNA polymerase, which is generated by the transcript RNA and temporarily forms a DNA-RNA hybrid with the DNA template chain, about 12 base pairs in length, forming a transcription bubble.
is 30-50 nucleotides per second, but not at a constant speed.
Looking at transcription under an electron
microscope
, it can be seen that on the same DNA template, a new synthetic RNA chain of different lengths is scattered into feathery graphics, indicating that there can be a very xinenable RNA polymerase in the same DNA gene at the same time catalytic transcription, generating the corresponding RNA chain. And longer RNA strands have been seen to adhere to the RNA body, forming a polyurucleosome. Explain that in some cases, the transcription process has not been completely terminated and translation has begun. phase of the transcription, there is not much difference between primary and uerical organisms. (iii) termination of transcription (termination) . Transcription is stopped at a certain location in the DNA template, people compare a number of pre-nuclear biological RNA transcription termination site near the DNA sequence, found that the DNA template transcription termination signal has two conditions, one is not dependent on protein factors to achieve termination effect, the other is dependent on protein cofactors to achieve termination, this protein cofactor is called a release factor, commonly known as ρ factor.
The two types of termination signals have common sequence characteristics, before transcription termination, there is an echo structure, the echo sequence is a sequence of opposite directions, the base complements each other, separated by several bases in this complementary sequence, not dependent on the termination sequence of ρ factors rich in G-C base pairs, its downstream 6-8 A ρ;
Its less travel is not due to fixed characteristics, the transcription of the resulting RNA can form a secondary structure, or shank structure, also known as hairpin structure, such a secondary structure may be embedded with a specific spatial structure of RNA polymerase, hindering the further function of RNA polymerase.
In addition to the termination signals of the DNA template itself, proteins found in the phage have helped RNA polymerases cross the termination site, called anti-transcription termination proteins, such as the N-gene product of the phage. is difficult to determine the 3' end of the original transcript because the urn is processed very quickly after RNA transcription. The termination site of the virus SV40 has been found to be much like E. coli's non-dependent ρ-factor terminator, and the transcripted RNA can form a hairpin structure with a series of U's at the end of the 3' .
3' end of the claw 5sRNA has four U's, and the sequence before and after them is a sequence rich in G.C. which is the termination signal for all urns of bioRNA polymerase III. transcription. This sequence characteristic is highly conservative, from
yeast
to human are very similar, any change that changes the characteristics of this sequence will lead to a change in transcription termination position.
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