RNA

From Big Medical Encyclopedia

RNA (RNA) — the phosphorus biopolymers having universal distribution in wildlife and being the integral component of all microorganisms, vegetable and zooblasts, and also many viruses. RNA represent one of two types, known in wildlife nucleic acids (see). Biol. the RNA function is connected with their central role in implementation of genetic information — the unique program of development of all signs and properties of each live organism. As carriers of hereditary information in most cases serve molecules DNA (see. Deoxyribonucleic acid ), however RNA can also carry out a similar role (a role genetic nucleinic to - you), napr, at viruses, providing in this case not only implementation, but also storage and hereditary transfer of the genetic program.

RNA represent high-molecular compounds with a line structure of molecules. Monomer units — ribonucleotides — are connected among themselves with the help of radio bonds between 5' - phosphate of one nucleotide and 3 '-a hydroxyl of the carbohydrate rest of the following nucleotide (5', 3 '-phosphodiester communication) and form a long stralght chain of a polyribonucleotide. The RNA carbohydrate component is presented by pentose — five-carbon sugar — a D-ribose (see. Ribose ), from here the initial name ribonucleic to - t — pentozonukleinovy to - you. The RNA nitrogenous components are heterocyclic bases, two of to-rykh derivative purine (see. Purine bases ) — adenine (A) and guanine (G) and two derivative a pyrimidine (see. Pirimidinovy bases ) — tsitozin (C) and uracil (U). Characteristic structural elements of nek-ry RNA are so-called minor bases; the nucleotides corresponding to them usually are a part of acceptor RNA (TRNK) and other RNA in very small amounts. Nitrogen bases are connected with the carbohydrate rest through its first (glycoside-ny) carbon atom. Purines join carbohydrate through a nitrogen atom in the provision 9 of a purine ring, pyrimidines — through a nitrogen atom in situation 3. The end of a chain bearing free or fosforilirovanny 5' - a hydroxyl of a ribose, call 5 '-the end, and the end of a chain containing free or fosforilirovanny Z' - a hydroxyl of a ribose,-3 '-the end of a molecule.

piece of a poliribonukleotidny chain of molecule RNA

Polynucleotide chains of RNA possess flexible structure, their length depending on a type of RNA can vary in very wide limits — from several tens to several tens of thousands nucleotide remains. Pier. weight (weight) of RNA on average 10 4 — 10 6 . The sequence of the nucleotide links connected by phosphodiester communication in a continuous and unbranched polynucleotide chain is called primary structure of RNA; it is strictly specific and unique for each type of natural RNA. Primary structure of RNA represents a form of record biol. information, repeatedly and the RNA which is precisely reproduced in processes of biosynthesis (see. Genetic code ). It causes a big variety of individual molecules RNA. Information on structure of protein in the form of the unique sequence of nitrogen bases of a polyribonucleotide is transferred from DNA (see. Transcription ) to to ribosomes (see) to be broadcast there in the corresponding sequence of amino acids (see. Broadcasting ).

The secondary and tertiary structure of RNA defined as spatial configuration of a polinukle-otidny chain forms generally at the expense of hydrogen bindings and interplanar hydrophobic interactions between nitrogen bases. If the steady spiral structure is characteristic of a molecule of native DNA, then the macro-molecular structure of RNA is much more variable also a labilna. In solutions with low ionic strength of molecule RNA behave as the typical strongly inflated chains of polyelectrolyte, but at increase in ionic strength these chains contract, their intrinsic viscosity decreases, and the speed of sedimentation increases. It is explained by education certain sites of a flexible chain of RNA, edge, being bent, is cast over itself, and double-helix structures as a result of the so-called complementary pairing similar to a complementarity in double-helix molecules DNA. Stabilization of such structures in RNA is reached due to formation of hydrogen bindings between opposite nitrogen bases of anti-parallel sites of a chain; specific base pairs between complementary sites of a chain are classical And — At, G — C and, more rare — At.

Existence in nitrogen bases of conjugated double bonds causes intensive absorption of RNA in the UF-spectral range with a maximum at wavelength apprx. 260 nanometers. Formation of a helical structure is followed by weakening of absorption at 260 nanometers (a so-called hypochromic change). Reverse — the destruction of double-helix structure happening at decrease in ionic strength of RNA solution or at its heating — is called molecular melting. It is explained by conformational transition a spiral —> a chaotic ball and is connected with weakening of the stabilizing interactions in molecule RNA. In this case the hyperchromic effect — increase in absorption is observed at 260 nanometers.

The molecules RNA consisting of two complementary polinukleo-tidny chains are found in nek-ry viruses of plants and animals. Besides, two-chained molecules RNA are formed as intermediate products of biosynthesis of many virus RNA in a cell; they are called replicative forms of RNA. In many parameters (in size of a step of a spiral, number of base pairs to a round — 11 — 12 couples, to corners of their inclination to an axis of a spiral, and also on a configuration of a sakharofosfatny skeleton) double-helix molecules or sites of molecules RNA are similar to double-helix molecules DNA in an A-form. Nek-ry dvutyazhevy RNA like DNA can exist in the form of ring molecules and if both polynucleotide chains are covalently closed, to form super-spiralizovannye rings. RNA is capable to formation of dvutyazhevy complexes, in to-rykh one of tyazhy another is presented poliribonukle-otidny, and — a polidezoksiribonukleotidny chain. Formation of such DNA — RNA hybrids happens during DNA replication to participation of inoculating fragments of RNA (see. Replication ), and also in the course of a transcription of RNA on a matrix of DNA. Besides, DNA — RNA hybrids form after infection of cells with the nek-ry RNA-containing viruses as a result of synthesis on virus RNA complementary to it DNA by means of virusospetsifichesky enzyme — the return transcriptase (see. Revertaza ).

The vast majority of natural RNA treats odnotyazhevy polynucleotides. However in polynucleotide chains of RNA there are sites of various length consisting of the nucleotide sequences complementary each other including from tens to thousands of the nucleotide remains and located on small removal from each other. Thanks to it in molecules RNA there are both the short, and very extended dvutyazhevy (bispiralny) sites belonging one chain, a so-called hairpin. The model of secondary structure of RNA with shpilkoobrazny elements was created in the late fifties — the beginning of the 60th of 20 century in A.S. Spirin and P. Doty's laboratories.

The first approaches to definition of the nucleotide sequence of RNA were developed in the mid-sixties 20 century in laboratories P. of Halle, H. Zachau and A. A. Bayev; it laid the foundation for the analysis of the structurally functional organization of individual RNA.

Content of RNA in living cells (except for spermatozoa) is much higher, than the content of DNA, and distribution in a cell is more difficult than them. The ground mass of RNA is localized in cytoplasm, they are a part of actually cytoplasmatic ribosomes (see), and also ribosomes mitochondrions (see) are also present at a free look or in the form of not ribosomal complexes with proteins. In a kernel of RNA are a component chromatin (see). A part of RNA of chromatin is a product of the current processes of a transcription of genes, including and regulatory (see. Gene ), however there are indirect and direct instructions on existence of special forms of the chromatinic RNA playing a regulatory role.

The majority of RNA of zooblasts, bacteria and DNA-containing of viruses is synthesized on a matrix of two-chained DNA in the course of a transcription. One-chained RNA of a number of viruses are formed on a matrix of two-chained RNA.

Matrix synthesis of one-chained RNA significantly differs from DNA replication and two-chained RNA: it is conservative, but not semi-conservative, i.e. the product of synthesis does not include any components of a matrix (see. Replication ). The conservative nature of synthesis and need to replicate not both chains of a matrix, but only one, and not throughout a matrix but only on certain sites cause existence of special mechanisms of recognition of the initsiatorny and terminatorny sequences defining the beginning and the end of synthesis of molecule RNA.

In a cell biosynthesis of RNA on a matrix of DNA is carried out by enzymes of a RNA polymerase (see. Polymerases ). In cells of eukaryotes at least three enzymes responsible for synthesis of the RNA different types are revealed. Unlike the studied DNA polymerases of a RNA polymerase show a certain specificity in relation to different matrixes and even sites of matrixes. The RNA polymerase catalyzes education 3', 5 '-phosphodiester bonds between monomeric ribonucleosides, using as substrates of a nukleozidtrifosfata. Synthesis begins with bonding between two mononucleotides, at the same time the first of them, as a rule, is a purine nucleotide. The growing polynucleotide chain of RNA is extended in >the direction 5 '-3'. The synthesized RNA is complementary to a matrix of DNA, and the order of inclusion of nucleotides in a chain of RNA is defined by the sequence of nucleotides in a matrix of DNA as patterns of formation of complementary chains are the cornerstone of matrix synthesis. As a rule, RNA are synthesized in the form of the molecules predecessors (pre-RNK) having the bigger molecular weight, than functionally active molecules. These molecules predecessors undergo multistage process of maturing — so-called posttranskriptsionny processing, to-ry comes down to cutting by specialized cellular enzymes of the nek-ry sequences and modifications of primary structure as a result of enzymatic methylation, dehydrogenation etc. of nitrogen bases, and also an isomerization of nucleotides.

The RNA functions in a cell are difficult and diverse. According to functional purpose and structural features in any cell distinguish three RNA main types: ribosomal RNA (RRNK), acceptor RNA (TRNK) and information, or matrix, RNA (IRNK). Except the specified RNA types, in cellular kernels and in cytoplasm in small amounts also other kinds of molecules RNA meet. It is established that in nek-ry cases they are predecessors of RNA of above-mentioned types. In cytoplasm and in a kernel there is a set of so-called small RNA, their functions are still unknown.

Ribosomal RNA has big molecular weight and is characterized by metabolic stability. It makes apprx. 80% of all cellular RNA. Allocate it from the cleared ribosomes or their subparticles by processing with water solution of phenol, to-ry denatures proteins and does them insoluble. On the weight of RRNK makes from 50 to 65% of all material of ribosomes. Ribosomes of all organisms consist of two subunits: small and big. RNA about a pier is a part of big subunit of a ribosome of cells of eukaryotes. it is powerful apprx. 1,65•10 6 (26 — 28S-PHK), in structure of small subunit — RNA about a pier. it is powerful apprx. 0,65•10 6 (18S-PHK). Big and small subunits of ribosomes of cells of prokariot contain RNA about a pier. it is powerful respectively apprx. 1,1•10 6 (23S-PHK) and apprx. 0,5•10 6 (16S-PHK).

Molecule RRNK serves in each subunit as if as a framework, ribosomal proteins are going to Krom; the created ribonukleo-proteidny complex — so-called ribonukleoproteidny tyazh (RNP-tyazh) — will be organized in a complex compact particle — actually ribosomal subunit. Concept RNP-tyazha as bases of the structural organization of a ribosome is developed in the 60th 20 century. A.S. Spirin.

Also RNA with rather low a pier is associated with ribosomes. it is powerful: 5S-PHK, containing apprx. 120 nucleotides and connected with big ribosomal subunit; such RNA is found in bacterial and zooblasts. Besides, at ribosomes of eukaryotes, as a rule, there is one more low-molecular RNA, so-called 5,8S-PHK, edges is quite strongly associated by means of hydrogen bindings with 28S-PHK of big ribosomal subunit. These RNA are structural components of a ribosome.

The role of RRNK in beloksinteziruyushchy system of a cell is not exhausted them by structural functions. Prokariot on 3 '-the end of a molecule 16S-PHK have a sequence rich with pyrimidines, complementary to the small site of IRNK located on 5' - the end of its molecule. Komplementarny pairing of these sites, apparently, promotes initial linkng of IRNK with a ribosome. It is not excluded that nek-ry sites of RRNK play a part in formation of the peptidil-transferazny center of a ribosome responsible for formation of peptide bonds at synthesis of protein.

Biosynthesis of RRNK in cells of eukaryotes happens in a kernel and is carried out with the participation of enzyme of a RNA polymerase of I. The genome of eukaryotes contains many copies of the genes coding RRNK; ribosomal genes are grouped in the form of tandem repetitions and localized in one or several chromosomes (see). These sites of a genome are a component nucleoproteid (see), forming kernels (see) — cellular organellas, in limits to-rykh RRNK is also synthesized. Formation of this RNA represents complex, multistage process. Molecules RRNK are synthesized in the form of the huge predecessor (pre-RRNK) about a pier. weighing 4-106 (45S-PHK), to-ry further is exposed to modification (methylation, an isomerization etc.) and specific splitting with formation of intermediate forms of mature RRNK. At the same time nearly a half of an initial molecule of the predecessor degrades. Ribonucleases (see), those sites of their nucleotide chains separating RRNK from predecessors, to-rykh are already not present in a ribosome, are studied few.

Acceptor RNA makes about 15% of total quantity of cellular RNA. These are rather low-molecular RNA: their nucleotide chains contain only 75 — 90 nucleotides, and a pier. weight is in limits 23 000 — 30 000. In view of the TRNK small size easily separate from molecules of other RNA, as a rule, much larger. This RNA type — the element of beloksinteziruyushchy system which is most studied in the molecular plan. For the majority of TRNK the full sequence of nucleotides in a molecule is defined.

The way of allocation of TRNK consists in processing of unicells or the homogenized fabrics water solution of phenol, sedimentation by alcohol with the subsequent department of RRNK, DNA impurity and polysaccharides. As a result receive drug of total TRNK. Fractionation of drugs of total TRNK is carried out by means of a number of the physical, chemical or combined methods.

Feature of TRNK distinguishing it from other RNA is rather high content of minor nucleotides. On the basis of data on primary structure of TRNK the model of secondary structure, the flat image a cut was offered and experimentally confirmed reminds a clover leaf. Comparison of structures of various TRNK organized in «a clover leaf» reveals a number of common features. In all these structures there are 4 two-chained spiral sites, 3 of to-rykh are the «hairpins» bearing loops from not coupled nucleotides; 3 '-and 5 '-the ends of a polynucleotide chain are united in the longest spiralizovan-ny site containing 7 base pairs, which is coming to the end with not coupled acceptor trinucleotide of ZZA, amino acid joins Krom. Opposite to the acceptor end the loop contains a trinucleotide an anti-codon, to-ry provides specificity of interaction with complementary to it a triplet codon in IRNK. The nucleotides forming an anti-codon are always located in the middle of a loop. Side loops, probably, play an important role in binding of TRNK about aminoacyl-TRNK-sintetazoy and with a complex a ribosome — and PH K.

The further research of structure of TRNK showed that native molecules have the compact form: separate double-helix «hairpins» of «a clover leaf» develop in specific tertiary structure, edges is close at all TRNK. Ability of TRNK to form crystals allowed to apply a method of the X-ray crystallographic analysis to studying of spatial structure of its molecule. In 1973 — 1975 tertiary structure of one of TRNK was deciphered in A. Rich's laboratories and A. Klug. According to Rich's model — Kluga macromolecule TRNK has the L-shaped form, and the main functional centers of a molecule — an anticodon loop and the acceptor end — are on its ends. The distance between them makes 7,6 nanometers. Interactions of nitrogen bases, other than those are responsible for stabilization of tertiary structure, to-rye cause complementary pairing according to Watson — to Shout.

The structure of TRNK differs in big conservatism that, apparently, is connected with high extent of its functional specialization. This class of molecules during biosynthesis proteins (see) performs function of adapters in relation to amino acids, to-rye by means of highly specific enzymes — aminoacyl-TRNK-sintetaz — attach to themselves this or that amino acid and transfer it to a ribosome. Linkng of amino acid with TRNK happens due to formation of a covalent bond between SOON-group of amino acid and the rest of a ribose Z '-trailer adenosine of TRNK. The enzyme which is carrying out this process — aminoacyl-TRNK-sintetaza — is capable «to learn» both amino acid, and TRNK corresponding to it.

There is the whole set of various TRNK, in Krom each TRNK is specific in relation to any one amino acid. In a cell there are about 20 various amino acids, however are established that in some cases for the same amino acid there are two or more — sometimes five or six — types of TRNK. Such TRNK are called isoacceptor TRNK.

During synthesis of polypeptide on a ribosome of TRNK «learns» specific aminoacyl-TRNK-sintetazu, from a cut it accepts the corresponding activated amino acid; then joins a codon of IRNK on a ribosome and by that provides strict specificity of the choice and embedding of amino acid in the amino-acid sequence of the growing polypeptide; after formation of a peptide bond of TRNK holds the growing polypeptide chain on a ribosome.

In a genome of E. coli there are several tens of genes controlling synthesis of TRNK. In cells of eukaryotes their number is much more; most likely, structural genes of TRNK are distributed on different chromosomes. The nucleotide chain of TRNK is synthesized in a kernel by means of enzyme of a RNA polymerase III and appears in cytoplasm in the form of the macromolecular predecessor, to-ry does not contain the metilirovanny bases. The predecessor is longer than functionally active TRNK and has a little less compact tertiary structure. Besides, in some cases the RNA polymerase builds a nucleotide chain without three last nucleotides: 3' - the end of each molecule TRNK which is coming to an end with a triplet of ZZA is formed later with the participation of special enzyme.

As well as RRNK, TRNK passes a stage of maturing, at the end a cut of molecule TRNK get final conformation. Process of transformation of the predecessor into TRNK comes down to cutting by special cellular enzymes of the additional sequences and to modification of primary structure. One of numerous types of modification is methylation of nucleotides with help TRNK-metilaz.

Information, or matrix, RNA makes very insignificant part of lump of cellular RNA, only 5 — 10%. Unlike RRNK ITRNK IRNK fraction is characterized by the expressed heterogeneity by the size of molecules (a pier. the weight of IRNK reaches to 2-106) since it represents set of the molecules programming synthesis of all cellular proteins. In this regard abundance of individual IRNK in total drug RNA can make thousand shares of percent.

While RRNK and TRNK are metabolic steady, IRNK in some cases, especially at prokaryotic organisms, is rather short-lived. Its nucleotide structure is close to composition of DNA emitted from the same organism. As a part of the majority of IRNK Polya's sequences covalently connected with Z '-the end of a molecule are found. Poliadenilo-vy «tail» of IRNK contains from several tens to hundreds of nucleotides and is idiosyncrasy of this RNA type.

A considerable part cytoplasmatic and PH K of a zooblast is localized in structure by the policy (on-liribosom), components to-rykh is the broadcast IRNK and the related group of the ribosomes which are at different stages of broadcasting and containing growing on-lipeptidnye a chain of different length. The polysom or their subfractions received one way or another are the main source IRNK, allocation a cut can be carried out by direct deproteinization of polyribosomes or after preliminary allocation of polisomny IRNP (ribonucleoprotein). Polya's presence in and RNA allows to apply the rational ways of its allocation from heterogeneous drugs RNA based on use of specific properties of Polya. In nek-ry cases the polyadenylated IRNK is allocated directly from unfractionated cytoplasmatic extract. These methods are based on formation of hydrogen bindings between Polya in both RNA and complementary oligo-or the polynucleotides immobilized on inert carriers. As such affine carriers (sorbents) apply poliu-sepharose and oligo (dezoksitimidin) - cellulose. Sometimes for allocation of IRNK use the selective sorption of the polia-containing IRNK on nitrocellulose-nykh filters or columns with chemically modified celluloses caused by abnormal sorption properties of an adenylic gomopoliribonukleotid.

From the structural signs characterizing almost any IRNK of animal origin it should be noted existence blocked metilirovanny 5' - the end, the so-called cap containing 7 methylguanine riboside connected with B '-a trailer nucleotide 5' — 5 '-trifosfatnym the bridge. The cap is necessary for effective initiation of synthesis of protein on IRNK and probably for protection of B '-the end of molecule IRNK from cellular ekzo-nucleases (see. Nucleases ). Between the cap and an initsiatorny codon of AUG defining the beginning of synthesis of a proteinaceous chain there is the 5th '-end-vaya a zone which is not broadcast in the sequence of amino acids. Further the broadcast, i.e. coding protein, area follows, length varies a cut over a wide range depending on molecular dimensions of the coded polypeptide. The broadcast IRNK area usually contains information for synthesis of several polypeptide chains in cells of prokaryotic organisms, i.e. belongs to so-called poly-cisthrone type. The segments of poly-cisthrone IRNK corresponding to each gene are broadcast separately thanks to existence between them intramolecular signals of initiation and termination of broadcasting. IRNK of zooblasts are, as a rule, monotsistronny-m. It is fair also for such IRNK, to-rye code formation of several polypeptide chains; formation of the mature polypeptides coded in such matrix is provided with post-transmitting proteolytic splitting of primary product of synthesis.

In Z' - a trailer zone of molecule IRNK between the terminatorny codon limiting the broadcast area, and Polya localized the nucleotide sequence of considerable length which is not bearing information on structure of the coded protein. Its function is not clear yet.

In studying of primary structure of IRNK noticeable success is achieved. Primary structure of IRNK and - and R-chains of hemoglobin of a rabbit and the person is completely established (see. Gemoglobin ), pro-insulin of a rat (see. Proinsulin ), chicken ovalbumin and many others. Definition of the nucleotide sequences of individual IRNK is of great interest. It is, in particular, a way of identification of mutant genes and interpretation of the molecular mechanisms which are the cornerstone of synthesis of abnormal proteins and genetic defects of regulation of protein synthesis at various forms of hereditary pathology of the person and animals. Circle of these patol. states it is rather wide. The malignant new growths which are followed by disturbance of a differentiation of cells and high-quality reorganization of work of a genome, various endocrinopathies with disturbances of regulation of synthesis of hormones, diseases of a liver with insufficiency of protein synthesis of blood serum, a disease of kidneys and anomalies of system of a blood coagulation concern to them. Quantitative defects of synthesis of individual proteins (insufficient or excess synthesis) play an important role in a pathogeny of these diseases. Hereditary pathology of synthesis of protein is studied most in detail, edges it is presented by heterogeneous group of defects of synthesis alpha or beta chains of a globin of hemoglobin. Assume that lack of activity of p-IRNK at a beta talassemia (see. Thalassemia ) it can be connected with a mutation in 5 '-the trailer area breaking linkng of IRNK with ribosomes or causing premature termination of proteinaceous synthesis.

Similar data were obtained also in case of Wilson's disease — Konovalova (see. Hepatocerebral dystrophy ), the wedge, manifestations a cut are connected with intoxication of a human body copper. Accumulation of copper in a toxic and neutiliziru-emy form is caused by genetically determined disturbance of synthesis of ceruloplasmin (see. Respiratory pigments ) — main cupriferous glycoprotein of a blood plasma. Quantitative insufficiency of this protein is explained probably by defect of the structural organization B' - the end of tserulo-plasmin IRNK, edges are defined both by linkng of IRNK with a ribosome, and synthesis of the alarm peptide sequence.

Nek-ry forms of hereditary pathology of a thyroid gland of the person as believe, are caused by anomaly in structure pre-IRNK, leading to disturbances its post-transkriptsionnogo processing and transfer in cytoplasm.

Various IRNK have the expressed secondary structure; about 75% of all nucleotide sequences of IRNK are involved in structure of two-chained sites. The considerable part of sites of secondary structure in IRNK is identified as «shpilechny» structures. Intramolecular sites of secondary structure are localized, apparently, both in the broadcast zone IRNK, and in Z '-a trailer and 5th '-game-tsevoy not broadcast parts of its molecule. The role of sites of secondary structure and implementation of the IRNK matrix functions is not established yet. Perhaps, they provide the adequate steric interaction of a cap and initiation codon necessary for their simultaneous participation in binding of IRNK on a ribosome. Assume also that «hairpins» play a role of the specific structures causing recognition of certain sites of IRNK proteinaceous components of nuclear and cytoplasmatic IRNP, so-called informosomes.

In a kernel and in cytoplasm of zooblasts of IRNK in a stand-at-ease it is not transferred, and always is in a complex with specialized proteins. Proteinaceous components differ in nuclear and cytoplasmatic RNP-particles: a part of nuclear carrier proteins leaves IRNK at the time of its transition to cytoplasm and is replaced with the transporting proteins of other type — cytoplasmatic informosomes are formed. Functions of informosomny proteins are not limited to intracellular transport of IRNK and protection it from damages; assume that they promote separation of neogenic IRNK from DNA of a matrix, its posttranskriptsionny maturing in a kernel, and also also PH K in cytoplasm play a regulatory role in processes of maturing and deposition nek-ry.

Cytoplasmatic and nuclear IRNP-particles were open and widely investigated in our country at the beginning of the 70th 20 century in A.S. Spirin and G. P. Georgiev's laboratories.

As well as all listed types of cellular RNA, IRNK represent population of the molecules «copied» from the respective sites genetic nucleinic to - you (most often DNA). However, if RRNK and TRNK belong to the servicing device of beloksintezi-ruyushchy system of a cell, then IRNK is a direct intermediary between DNA and proteins and is a matrix for synthesis of the last. Thus the most part of information which is contained in DNA is transferred to the IRNK form.

In bacterial cells even before completion of synthesis of molecule IRNK its broadcasting can begin: ribosomes contact the separated ready site of IRNK and form to polysom, synthesizing protein. In zooblasts of the place of synthesis of protein and RNA spatially are separated: IRNK is synthesized in a cellular kernel in the form of the huge predecessor (pre-IRNK). In addition to the sequence of IRNK, in molecules pre-IRNK there is a large number of the sites performing regulatory and various support functions. Molecules pre-IRNK have no cap and polyadenylic «tail» — the last is increased right after end of a transcription by means of the so-called bezmatrichny synthesis catalyzed trailer poli-A-sintetazoy. From a kernel pre-IRNK as a part of RNP-particles — informosomes — it is transported in cytoplasm. In the course of an exit pre-IRNK in cytoplasm the main part of the auxiliary nucleotide sequences in it collapses — the molecule undergoes a number of very essential structural transfomations including formation of a cap, specific fragmentation, methylation, an isomerization etc., i.e. posttranskriptsionny processing.

Idiosyncrasy of many pre-IRNK eukaryotes is existence in information zone of a molecule of not coding sites — introns, the sizes to-rykh can be very considerable; quantity of such inserts which are not bearing information for synthesis of protein in different genes variously. The difficult internal topography of molecules pre-IRNK causes a difficult picture of consecutive reactions of posttranskriptsionny maturing and formation of mature IRNK, the coding zone a cut is continuous and does not contain introns. Highly specific processes of cutting not coding inserts of a molecule pre-IRNK and their associations (stitching) received the name splicing. Fermental system of splicing, and also it biol. a role remain still absolutely unexplored.

Histochemical methods of definition of RNA in fabrics. In a basis gistokhy. methods of identification of RNA in fabrics and cells reactions to the components which are formed as a result of hydrolysis of these to - t lie. In a kernel and cytoplasm usually apply Brashe's method, essence to identification of RNA to-rogo consists in a specific depolymerization of RNA ribonuclease, DNA at the same time is not mentioned. Two cuts of fabric are in parallel used, from to-rykh one previously is affected by ribonuclease. Then both cuts paint imperial green — pyronin, to-ry has elective affinity to RNA. Consider that the material which is painted pyronin in red color and disappearing after processing by ribonuclease represents RNA. Cuts it is possible to paint also 1% water solution of toluidine blue or 1% solution toluidine blue in 95% alcohol; RNA at the same time are painted in blue color. For identification not only RNA, but also their communication with structures of a cell after coloring toluidine blue cuts dokrashivat 2% solution of orange G in 5% phosphatotungstic to - those.

Except Brashe's method, for identification of RNA use the dye carrying the name gallotsionin-chrome alum, to-ry gives the steady coloring which is not changing at dehydration in alcohol and an enlightenment in a xylol. Coloring it is possible to carry out at any pH values ranging from 0,8 to 4,3, but at low pH values (1,5 — 1,75) specific coloring of RNA as much as possible. Nek-ry researchers consider a method of identification of RNA by means of dye gallotsionin-chrome alum more reliable, than Brashe's method. It is used also for quantitative gistokhy. definitions nucleinic to - t.

Apply to studying of synthesis and exchange of RNA also a gistoavtoradiografiya often in combination with electronic autoradiography (see). As a radioactive label use 3H-uracil.

At gistokhy. studying of localization of RNA in individual cells or on fabric cuts the purine and pirimidinovy bases reveal on absorption intensity in UF-light. Nucleinic to - you thanks to existence of the heterocyclic purine and pirimidinovy bases intensively absorb UF-light with the wavelength of 260 nanometers. At photography of cells in these beams of structure, containing nucleinic to - you, are identified quite easily. However by means of this method it is impossible to carry out direct differential definition of DNA and RNA.

Localization of RNA in cells and cuts can be determined by a carbohydrate component. After soft hydrolysis salt to - that, causing eliminating of purine bases and release of reactive aldehydic groups of the rest of sugar, carry out reaction with metiltrioksifluorenony. At the same time the RNA carbohydrate component — a ribose — reacting with dye, forms the connection painted in yellow-pink color.

Histochemical RNA identify also on identification phosphoric to - you. Phosphatic groups nucleinic to - the t can be determined by coloring by the main dyes selectively. E.g., use of acrolein and toluidine blue in the presence of RNA leads to emergence of gentle-red coloring (DNA in these conditions gives dark blue color). Cresylic violet you react RNA in stoichiometric quantities at pH 4,2 and therefore it can be used for cytophotometric quantitative definition of RNA using UF-mikrospektrofotometriya (see. Spektrofotometriya , Cytophotometry ).



Bibliography: Gaytskhoki V. S. Information RNA of zooblasts, M., 1980, bibliogr.; Davidson D. N. Biokhimiya of nucleic acids, the lane with English, M., 1976; Organic chemistry of nucleic acids, under the editorship of N. K. Kochetkov and E. I. Budovsky, M., 1970; Spirin A. S. and Gavrilova JI. P. Ribosoma, M., 1971; Watson J. D. Molecular biology of a gene, the lane with English, M., 1978; Shabarova 3. And. and Bogdanov of A. A. Himiya of nucleic acids and their components, M., 1978; Akzesso-rische Methoden in der Histochemie, hrsg. v. G. Geyer u. H. Luppa, Jena, 1975; Bra-ch et J. Embryologie chimique, P., 1944; Culling Ch. F. A. Handbook of his-topathological and histochemical techniques, L., 1974; Pearse A. G. Histochemistry, v. 1—2, L., 1968 — 1972.


P. L. Ivanov; V. V. Serov (gist.).

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