What is RNA interference? By this term is meant a system for controlling the activity of genes of eukaryotic cells. A similar process occurs due to short (no more than 25 nucleotides in a chain) ribonucleic acid molecules.
RNA interference is characterized by post-transcriptional inhibition of gene expression through the destruction or deadenylation of mRNA.
Relevance
It was found in the cells of many eukaryotes: fungi, plants, animals.
RNA interference is considered an important way to protect against cell viruses. She takes part in the process of embryogenesis.
Due to the powerful and selective nature of the influence of ribonucleic acid on gene expression, serious biological studies can be carried out in living organisms and cell cultures.
Previously, RNA interference had a different name - cosuppression. After a detailed study of such a process, receiving Andrew Fire and Craig Melo Nobel Prize in medicine for studying the mechanism of its course, this process was renamed.
Story
What is RNA interference? Its discovery is due to serious preliminary observation under the influence of antisense RNA-inhibition of expression in plant genes.
After some time, American scientists obtained amazing results when transgenes were introduced into petunia. Researchers tried to modify the analyzed plant in such a way as to give the flowers a more saturated shade. To do this, they introduced additional copies of the gene of the enzyme chalcone synthase into the cells, 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 color of the corolla of the petunia, the flowers of this plant turned white. A decrease in the activity of the enzyme of chalcone synthase was called cosupresia.
Important points
Subsequent 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 insensitive to virus infection. It was experimentally established that obtaining such resistance is achieved by introducing into the plant gene a short non-coding sequence of viral RNA.
RNA interference, the mechanism of which is still not fully understood, has been called "virus-induced suppression of gene expression."
The biologists began to call the sum of such phenomena post-transcriptional inhibition of gene expression.
Andrew Fayer and his colleagues were able to prove the connection between a similar phenomenon and the introduction of a combination of sense RNA and antisense RNA forming double-stranded. It was she who was recognized as the main reason for the appearance of the described process.
Features of molecular mechanisms
The Dicer protein Giardia intestinalis is catalyzed by cutting double-stranded RNA to produce small interfering RNA fragments. The RNA domain has a green color, the PAZ domain is yellow, and the binding helix has a blue tint.
The use of RNA interference is based on the exogenous and endogenous pathways.
The first mechanism is based on the genome of the virus or is the result of laboratory experiments. There is a cut in the cytoplasm of such RNA into small fragments. 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 structures of the stem loop inside the nucleus, forming mRNAs that interact with the RISC complex.
Small interfering RNA
They are chains consisting of 20-25 nucleotides having nucleotide protrusions at the ends. Each chain has a hydroxyl moiety at the 3'-end and a phosphate moiety at the 5'-part. A structure of this kind is formed as a result of the action of the Dicer enzyme on RNAs 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” chain in the RISC. It allows the effector complex to search for a specific mRNA target. Upon attachment of the siRNA-RISC complex, mRNA degradation occurs.
Such molecules hybridize with one type of target mRNA, which leads to cleavage of the molecule.
mRNA
RNA interference and plant protection are interrelated processes.
mRNA consists of 21-22 sequentially linked nucleotides of endogenous origin, which are involved in the individual development of organisms. Its genes are transcribed, forming long primary pri-miRNA transcripts . These structures have the form of a loop stalk; their length consists of 70 nucleotides. They contain an enzyme with RNA activity of basics, as well as a protein capable of binding double-stranded RNA. Next, transport is carried out to the cytoplasm, where the resulting RNA becomes a substrate for the Dicer enzyme. Processing may occur in different ways, depending on the type of cell.
This is how RNA interference proceeds. The application of the process is still not fully understood.
For example, it was possible to establish the possibility of a different path of mRNA processing, which does not depend on Dicer. In this case, the molecule is cut by a protein by an argonaut. The difference between miRNA and siRNA is the ability to inhibit translation with several different mRNAs that contain similar sequences of amino acid units.
Effector complex RISC
RNA interference, the biological functions of which allow one to solve many issues related to the protein complex, which ensures mRNA cleavage during interference. The RISC complex promotes the separation of ATP into several fragments.
Using X-ray diffraction analysis, it was determined that through such a complex the process is significantly accelerated. Argonaut proteins, which are localized in certain places of the cytoplasm, are considered its catalytic part. Such R bodies represent regions with significant levels of RNA degradation; it is in them that the highest mRNA activity was revealed. The destruction of such complexes is accompanied by a decrease in the efficiency of the RNA interference process.
Transcriptional Inhibition Methods
In addition to acting at the level of translation inhibition, RNA also affects the transcription of genes. Some eukaryotes use this pathway to ensure the stability of the genome structure. Due to the modification of histones, gene expression can be reduced in a certain area, since such a piece is converted to heterochromatin.
RNA interference and its biological role is an important issue that deserves serious study and analysis. For the study, those sections of the chain that are responsible for the type of mating are considered.
For example, for yeast, transcription suppression is carried out precisely by the RISC complex, which contains a Chp1 fragment with a chromodomain, an argonaut, and also a protein with an unknown Tas3 function.
For the induction of the formation of heterochromatin sites to occur, the Dicer enzyme, RNA polymerase, is required. The division of such genes leads to disruption 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 adenosine conversion into inosine, which occurs in the double RNA chain. To carry out such a conversion, 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 molecular editing were recognized as competitive processes. Studies in mammals suggest that RNA editing can prevent transgene suppression.
Differences between organisms
It lies in the ability to perceive foreign RNA, to use them in the course of interference. For plants, this effect is systemic. Even in the case of insignificant administration of RNA, a certain gene is inhibited throughout the body. With this action, the RNA signal is transmitted between the remaining 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, siRNA transport occurs via plasmodesmata. Inheritance of such RNA effects is provided by methylation of promoters of certain genes.
The main difference between such a mechanism in plants is the ideality of mRNA complementarity in them, which, together with the RISC complex, contributes to the complete degradation of this molecule.
Biological functions
The system under consideration is an important component of the immune response to foreign materials. For example, plants have several Dyser protein analogues that are used to fight numerous viral organisms.
RNA can be considered an antiviral defense mechanism acquired by plants that run throughout the body.
Despite the fact that much less Dyser protein is expressed in animal cells, we can talk about the participation of RNA in the antiviral response.
Currently, the immune reactions that occur in humans and animals have been partially studied.
Biologists continue research, trying not only to justify the mechanisms of their course, but also to find ways to influence immune interactions. In the case of a successful explanation of all the nuances of RNA interference, scientists will have the opportunity to manage these biochemical reactions, create protection mechanisms from foreign bodies.