POKSVIRUSA

From Big Medical Encyclopedia

POKSVIRUSA (Poxviridae; English pox a pustule + viruses) — family of large DNA-containing of viruses.

Earlier P. called viruses of smallpox. Item the largest viruses. They are capable to infect mammals, including the person (see. Smallpox of animals, at the person ), birds, fishes, amphibians and even insects. This family includes nine childbirth (tab).

Virion P. of a kirpicheobrazny or ovoidny form, has the sizes 300 — 450 nanometers of X 150 — 260 nanometers. The core of virion represents DNA associated with proteins. This structure is put into the fibrous casing constructed of well distinguishable subunits and has difficult symmetry. The outside cover of virion contains lipids and is covered with the tubular or filamentary proteinaceous structures organized in characteristic twisted spirals. Under an outside cover lateral bodies, function are located to-rykh it is not found out. In virions P. it is revealed apprx. 100 virusospetsifichesky proteins, a part from to-rykh is glycoproteins. At least 10 of them have enzymatic activity. Among them DNA-dependent the RNA polymerase is, weed (And) - a polymerase, a MRNK-guaniltransferaza, MRNK-(guanine-7) methyltransferase, MRNK-(a ribose-2') methyltransferase, the Tax Code-dependent a nucleoside triphosphate of a fos-fogidrolaza, a deoxyribonuclease (one of three, found in virion), a protein kinase, the enzyme recovering ruptures of DNA, etc. Availability of enzymes allows P. to carry out a transcription of DNA at early stages without participation of enzymes of a host cell.

P.'s genome represents uniform two-chained molecule DNA about a pier. it is powerful (weighing) 130 — 240 X 106 dalton; content of guanine + a tsitozina at poksvirus of vertebrata makes 35 — 40%, and at poksvirus of insects — apprx. 26%. DNA of poksvirus has no infectivity. During the processing of DNA isolated from virions P., by bacterial restriktaza of DNA it is split on fragments, quantity and the sizes to-rykh are various at separate Items. This method of the analysis is used during the studying of an origin nek-ry P. and their belonging to a certain sort.

P. of vertebrata have at least one antigen which is an internal component of virion which gives cross serol. reaction with representatives of all Items. In each genus P. of vertebrata reactions are observed accurate cross serol.

P.'s reproduction occurs in cytoplasm of the infected cell though there are data that synthesis of virusospetsifichesky RNA can be carried out also in kernels. At penetration of a virus into a cell under the influence of enzymes of a host cell the outside cover of virion collapses (deproteinization). After release of a nucleocapsid from an outside cover the virionny DNA-dependent RNA polymerase carries out transcription (see) from virionny DNA of preearly MRNK. Further deproteinization of virionny DNA happens to participation of one of the proteins which are broadcast from these MRNK. From completely deproteined DNA additional sites are transcribed and early MRNK are formed. At the same time DNA replication begins, and from affiliated molecules DNA late MRNK are transcribed. During the early period slightly less than 50% of all genetic information coded in DNA are transcribed, and at a late stage 100% of a genome since at this stage not only late, but also early MRNK are synthesized are transcribed. In the infected cells a large amount of proteins is synthesized, at the same time, in addition to the proteins which are afterwards a part of virion, at early stages at least 50 nonstructural proteins are formed. Accurate regulation of synthesis of a number of virusospetsifichesky proteins is found in P., edges it is carried out not only at the level of a transcription, but also at the level of broadcasting as a part of virusospetsifichesky proteins P. is synthesized in the form of large polypeptides-prepole-vennikov which are split on smaller functional proteins. Assembly of virions P. happens in the special cytoplasmatic structures which received the name of «factories».

High frequency is characteristic of P. recombinations (see), and also typical for viruses only this family a phenomenon which received the name of not genetic reactivation (see. Not genetic interactions of viruses ); this phenomenon is observed at P.'s interaction vertebrata both within a sort, and between representatives of various childbirth. At P. the mutants differing on a number of properties are received and described: to the size and the nature of defeats chorion-allantoisnoy of a cover of a chicken embryo (e.g., the so-called white mutants of viruses of smallpox of rabbits, cows, monkeys forming white pockmarks on chorion-allantoisnoy to a cover unlike the pockmarks of red color caused by parent strains); by the size and character of the plaques formed on culture of fabric; abilities to a reproduction at an elevated temperature; resistance to physical. - to chemical influences, etc. Conditional and lethal mutants of P. (temperature and sensitive and dependent on a host cell) which with success are used during the studying of mechanisms of a reproduction of these viruses are received.

At animal P.' infection most often there are skin defeats in a type of rash of papular and pustular character. The virus of smallpox of monkeys causes in them at a natural disease a wedge, manifestations of two types: hypostasis of a front part of the head and neck which can lead to death from asphyxia, and skin not gene-ralizovannye of defeat. At the smallpox of mice caused by a virus of an ektromeliya either skin, or internals are surprised. Are most characteristic at this disease of damage of skin of extremities, coming to an end with a necrosis and rejection of a part of an extremity. The virus of smallpox of rabbits has high pathogenicity for these animals, and the disease often comes to an end with a lethal outcome. Parapoksvirusa of hoofed animals can strike also the person, causing, e.g., the disease which is followed by emergence of small knots on skin of hands (small knots of doilshchitsa). Viruses of smallpox of birds cause diseases, at to-rykh skin defeats have proliferative character, partly similar to the course of tumors. Typical tumors develop at defeat of a leporipoksvirusama — viruses of a myxoma and fibroma of rabbits, and also a virus of monkeys of Yaba which can cause formation of tumors and at the person. The virus of a contagious mollusk is also capable to cause small tumors of skin in the person. The greatest value for pathology of the person has a virus of natural smallpox (see. Smallpox natural ). This disease is completely liquidated around the world thanks to a highly active live bovine vaccine (see. Smallpox vaccination ), and also a number of organizational actions for identification of the centers of a disease, vaccination and so forth which were carried out under the auspices of WHO with active participation of specialists from the Soviet Union and during the use of millions of doses of the smallpox vaccine made in our country.

Table. CLASSIFICATION POKSVIRUSOV




Bibliography: Gendonum Yu. 3. Molecular genetics of viruses of the person and animals, page 125, M., 1975; Zhdanov V. M. and Gaydamovich of S. Ya. Virusologiya, page 195, etc., M., 1966; Fenner F., etc. Biology of viruses of animals, the lane with English, t. 1, page 131, M., 1977; Fenner F. Classification and nomenclature of viruses, Intervirology, v. 7, p. 8, 1976; it, Portraits of viruses, poxviruses, ibid., v. 11, p. 137, 1979.


BB. 3. Gendonum.

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