What is RNA interference? This term refers to a system for controlling the activity of genes in eukaryotic cells. A similar process occurs due to short (no more than 25 nucleotides per chain) molecules of ribonucleic acid.
RNA interference is characterized by post-transcriptional inhibition of gene expression through the destruction or deadenylation of mRNA.
Significance
It was found in the cells of many eukaryotes: fungi, plants, animals.
RNA interference is considered an important way to protect cells from viruses. She takes part in the process of embryogenesis.
Due to the powerful and selective nature of the effect of ribonucleic acid on gene expression, serious biological research can be carried out in living organisms, cell cultures.
Previously, RNA interference had a different name - cosuppression. After a detailed study of this process, receiving the Nobel Prize in Medicine for the study of the mechanism of its occurrence by Andrew Fire and Craig Melo, this process was renamed.
History
What is RNA interference? Its discovery is due to serious preliminary observation under the influence ofantisense RNA inhibition of expression in plant genes.
Some time later, American scientists obtained amazing results when transgenes were introduced into petunias. The researchers tried to modify the analyzed plant in such a way as to give the flowers a more saturated hue. To do this, they introduced into the cells additional copies of the gene for the enzyme chalcone synthase, which is responsible for the formation of the purple pigment.
But the results of the study were completely unpredictable. Instead of the desired darkening of the corolla of the petunia, the flowers of this plant have become white. Decreased activity of the enzyme chalcone synthase has been termed cosuppression.
Important points
Following experiments revealed the effect on this process of post-transcriptional inhibition of gene expression due to an increase in the level of mRNA degradation.
At that time it was known that those plants that express special proteins are not susceptible to infection by the virus. It has been experimentally established that obtaining such resistance is achieved by introducing a short non-coding sequence of viral RNA into the plant gene.
RNA interference, the mechanism of which is still not fully understood, has been called “virus-induced gene silencing.”
Biologists began to call the sum of such phenomena post-transcriptional inhibition of gene expression.
Andrew Fire and his colleagues managed to prove the connection between a similar phenomenon and the introduction of a set of semanticRNA and antisense forming double-stranded RNA. It was she who was recognized as the main reason for the appearance of the described process.
Features of molecular mechanisms
The Giardia intestinalis Dicer protein is catalyzed by cutting double-stranded RNA to produce small interfering RNA fragments. The RNAase domain is green, the PAZ domain is yellow, and the binding helix is blue.
The application of RNA interference is based on exogenous and endogenous pathways.
The first mechanism is based on the virus genome or is the result of laboratory experiments. Such RNA is cut into small fragments in the cytoplasm. The second type is formed during the expression of individual genes of a living organism, for example, pre-micro RNA. It involves the creation of specific stem-loop structures within the nucleus, forming mRNAs that interact with the RISC complex.
Small interfering RNAs
They are chains consisting of 20-25 nucleotides with nucleotide protrusions at the ends. Each chain has a hydroxyl moiety at the 3' end and a phosphate group at the 5' moiety. A structure of this type is formed as a result of the action of the Dicer enzyme on RNA containing hairpins. After cleavage, the fragments become part of the catalytic complex. The argonaut protein gradually unwinds the RNA duplex, which contributes to leaving only one “guide” strand in RISC. It allows the effector complex to search for a specific target mRNA. When joiningsiRNA-RISC complex mRNA degradation occurs.
These molecules hybridize with one type of target mRNA, resulting in cleavage of the molecule.
mRNA
RNA interference and plant protection are interrelated processes.
mRNA consists of 21-22 consecutive nucleotides of endogenous origin, which are involved in the process of individual development of organisms. Its genes are transcribed to form long primary transcripts of pri-miRNA transcripts. These structures have the form of a stem-loop, their length consists of 70 nucleotides. They contain an enzyme with RNase activity, as well as a protein capable of binding double-stranded RNA. Further, transportation to the cytoplasm takes place, where the resulting RNA becomes a substrate for the Dicer enzyme. Processing may take place in different ways, depending on the type of cell.
This is how RNA interference works. The application of the process has not yet been fully explored.
For example, it was possible to establish the possibility of a different path of mRNA processing, which does not depend on Diser. In this case, the molecule is cut by the argonaut protein. The difference between miRNA and siRNA is the ability to inhibit translation with several different mRNAs that contain similar amino acid sequences.
RISC effector complex
RNA interference,the biological functions of which allow solving many issues related to the protein complex, which ensures the cleavage of mRNA during interference. The RISC complex promotes the division of ATP into several fragments.
With the help of X-ray diffraction analysis, it was determined that by means of such a complex the process is significantly accelerated. Its catalytic part is considered to be argonaut proteins, which are localized in certain places in the cytoplasm. Such P-bodies represent areas with significant levels of RNA degradation; it is in them that the highest mRNA activity was detected. The destruction of such complexes is accompanied by a decrease in the efficiency of the RNA interference process.
Methods of transcription suppression
In addition to its action at the level of translational inhibition, RNA also has an effect on gene transcription. Some eukaryotes use this way to ensure the stability of the genome structure. Thanks to the modification of histones, it is possible to reduce gene expression in a certain area, since such a piece passes into the form of heterochromatin.
RNA interference and its biological role is an important issue that deserves serious study and analysis. To conduct research, those sections of the chain that are responsible for the type of pairing are considered.
For example, for yeast, transcription suppression is carried out precisely by the RISC complex, which contains the Chp1 fragment with the chromodomain, argonaut, and a protein that hasunknown function Tas3.
In order to induce the formation of heterochromatin regions, the Dicer enzyme, RNA polymerase, is required. The division of such genes leads to a violation of histone methylation, leads to a slowdown in cell division, or a complete stop of this process.
RNA editing
The most common form of this process in higher eukaryotes is the process of converting adenosine into inosine, which occurs in the double strand of RNA. To carry out such a transformation, the enzyme adenosine deaminase is used.
At the beginning of the twenty-first century, a hypothesis was put forward, according to which, the mechanism of RNA interference and editing of the molecule were recognized as competitive processes. Mammalian studies suggest that RNA editing can prevent transgene silencing.
Differences between organisms
It lies in the ability to perceive foreign RNA, apply them in the course of interference. For plants, this effect is systemic. Even in the case of a slight introduction of RNA, a certain gene is suppressed throughout the body. With this action, the RNA signal is transmitted between other cells. RNA polymerase takes part in its amplification.
Between organisms there is a difference in the use of foreign genes in the process of RNA interference.
In plants, the process of siRNA transport occurs through plasmodesmata. The inheritance of such RNA effects is ensured by methylation of the promoters of certain genes.
The main difference between this mechanism andplants is the ideality of their mRNA complementarity, which, together with the RISC complex, contributes to the complete degradation of this molecule.
Biological functions
The system in question is an important component of the immune response to foreign materials. For example, plants have several analogues of the Dicer protein, which are used to fight numerous viral organisms.
RNA can be considered a plant-acquired antiviral defense mechanism that is triggered throughout the body.
Despite the fact that much less Dicer protein is expressed in animal cells, we can talk about the participation of RNA in the antiviral response.
Currently, the immune responses occurring in the body of humans and animals have been partially studied.
Biologists continue research, trying not only to substantiate the mechanisms of their occurrence, but also to find ways to influence immune interactions. In case of a successful explanation of all the nuances of RNA interference, scientists will be able to control these biochemical reactions and create mechanisms of protection against foreign bodies.
