From Big Medical Encyclopedia

REVERSION (Latin reversio turn, return; synonym the return, or returnable, mutation) — complete or partial recovery of initial phenotypical manifestation of the gene lost or changed as a result of a mutation. The individual, in a cut occurred R., call a revertant.

The river arises under the influence of the same factors, to-rye cause emergence of direct mutations (see. Mutagens ), also provides «correction» of various mutations in genes of various organisms, including willows genes of the person. R.'s studying is of special interest in connection with development of ways of correction of the mutations arising in genes of the formative cells and leading to hereditary diseases at posterity. Besides, determination of frequency of R. at nek-ry microorganisms is widely used in various experimental test systems at a research of mutagen activity of chemical substances, including pharmaceuticals, nutritional supplements, pesticides, etc. However the frequency of emergence of R. is quite low and in many cases does not exceed the frequency of the corresponding natural direct mutations.

The mechanism P. is studied at bacteria and viruses in detail, however there is an assumption that this mechanism is universal. The river eventually leads to complete or partial recovery of the functional activity of the molecule of protein lost or changed as a result of a straight line mutations (see) in the gene coding synthesis of this protein. The river results from recovery of a reference state of a gene (so-called true reversion) or at the expense of an additional (suppressor) mutation, the edge is not corrected by genetic defect, and suppresses (supressirut) its phenotypical manifestation.

«True» reversion consists in exact recovery of the initial sequence of nucleotides in the site of molecule DNA and, thus, in recovery of the sequence of the amino-acid remains in a polypeptide chain of protein, synthesis to-rogo is coded by that piece of DNA (genome) where there was R. E.g., inclusion of aminopurine in molecule DNA instead of adenine (A) can lead to emergence of the direct mutation consisting in replacement of one couple of nucleotides adenine — thymine (T) on another — guanine (G) — tsitozin (C), i.e. And — T -> G — C. As a result instead of the rest of one amino acid the polypeptide chain will join the rest of other amino acid that can cause change of functional properties of a proteinaceous molecule. If the changed site of DNA joins bromouracil, then there can be the return replacement of nucleotide couple of G — C -> And — T and recovery of the initial amino-acid sequence in a molecule of synthesizable protein since thanks to R. caused by bromouracil the structure of the initial triplet coding inclusion in a polypeptide chain of initial amino acid (is recovered see. Genetic code ).

The rubles arising at the expense of suppressor mutations are also of great interest. Two classes of suppressor mutations (suppressors) — intragenic (direct) and extra gene are known (indirect). Intragenic suppressor mutations arise in the same gene, in Krom there was direct mutation therefore the functions of a proteinaceous molecule lost as a result of direct mutation without recovery of its initial structure and a configuration are in whole or in part recovered. Loss of a nucleotide from a chain of DNA (suppressor mutation) can be an example of such mutation, in to-ruyu the additional nucleotide (direct mutation) breaking normal reading of genetic information until the end of this gene (so-called shift of a phase of reading) was built in earlier. As a result of suppression there is possible a synthesis of the protein which is not differing (or slightly different) from initial protein on the functional activity since replacement of one amino acid by another in polypeptide in nek-ry cases does not influence or almost does not influence secondary, tertiary and quarternary structure squirrel (see Proteins). In not gene suppressors do not mention those genes, in to-rykh there were direct mutations, but change other genes, turning them into genes suppressors. The product of a gene suppressor — the changed protein, in one way or another compensates the disturbances caused by direct mutation in work of other gene, without correcting genetic defect. Separate genes suppressors are found, under control to-rykh are synthesized acceptor RNA with the changed specificity of an attachment to information RNA that leads to correction of functional defect of mutant protein in the course of its biosynthesis.

As R. reduce the actual frequency of manifestation of various direct mutations, the further research of features pkh manifestations and frequencies of emergence at the person is necessary. Clarification of a role of various genes of the person and environmental factors in emergence and functioning of suppressors of various mutations the, and also the factors either breaking these processes or strengthening action of suppressors is of special interest.

At R.'s studying use modern genetic, biochemical, biophysical and other methods of a research. For the characteristic and differentiation of the «true» reversions and R. occurring at the expense of suppressor mutations definition of the sequence of the amino-acid remains in molecules of the proteins synthesized under control of the corresponding genes after direct mutation and after reversion is carried out. By means of the genetic analysis at bacteria of nek-ry types mapping of a number of gene suppressors is carried out, i.e. their localization on a bacterial chromosome is defined.

Bibliography: Ashmarin I. P. Molecular biology, page 199, etc., L., 1977; Bochkov N. P. Genetics of the person, Heredity and pathology, page 146, M., 1978; - Bresler S. E. Molecular biology, page 440, L., 1973; e r sh e N-z about S. M N. Fundamentals of modern genetics, Kiev, 1979; G.'s Stent and To e-l and N d and r River. Molecular genetics, the lane with English, page 158, 383, M., 1981.

V. P. Shchipkov.