PHAGE LAMBDA

From Big Medical Encyclopedia

PHAGE LAMBDA (phage of X; the Greek phagos devouring) — the temperate backteriophage specific to colibacillus.

T. l. is the reference representative of extensive taxonomical group of the lambdoidny phages differing in ability to induction under the influence of UV rays, a possibility of a recombination in cross crossings and similarity in the sequence of nucleotides of trailer sites of molecules of their DNA. Assume a community of an origin

of lambdoidny phages.

Studying F. l. played an outstanding role in formation and development of molecular genetics and biology, genetic engineering.

The consistent patterns determined at a research F. l., recombinations (see), a transcription are the cornerstone of modern ideas of molecular mechanisms of replication (see), (see), find applied

application during the designing of recombinant molecules.

T. l. E. Lederberg is described in 1951. Virion of a phage represents an isometric many-sided head of an ikosaedrichesky form the size apprx. 55 nanometers with a shoot 150 nanometers long and

7 — 12 nanometers wide. The capsid of a head is constructed

generally of 420 copies of protein about a pier. it is powerful (weighing) 38 000 and 415 copies protein about a pier. weighing 11 000.

The shoot consists of a flexible hollow core with fibrilla on the end, has no sokratshmy cover, joins a capsid of a head a distinguished neck and on structure reminds the disks laid by a pile. In a capsid around a belkovopodobny kernel (presumably, internal protein) one molecule DNA — a linear two-chained molecule about a pier is located. it is powerful apprx. 30,8 X 106. The homology of the nucleotide sequences of DNA of a phage a lambda and related phages in the sum makes 35 — 60% of the total molecular length and is presented by certain sites. On both ends of a molecule there are one-chained mutually complementary sites from 12 nucleotides (the sticky ends) providing a possibility of transformation of the DNA linear form to ring structure.

At infection of bacteria with a phage of its DNA it can be replicated in cytoplasm as an autonomous element or to be integrated in a zarep-ressirovanny state into a chromosome and to be replicated as its component (prophase) under genetic control of a bacterium. The recombination is carried out in the websites (sites) of a mutual attachment, specific to DNA of a phage and a cell, is followed by their physical gap and the subsequent reunion with formation of complete genetic structure of a cell with built in it in the DNA linear form of a phage.

The website-specific integration recombination is carried out in the absence of the expressed nucleotide homology in the websites with specific participation of the protein controlled by a genome of a phage. The repressor determined by a prophase, interacting with two of its loci, interferes in a cell of an expression (manifestation) of its genes, autonomous replication of its DNA, promotes emergence of specific immunity of a cell and supports its lysogenic state (see the Lysogeny) in unlimited number of generation with the inherited potential ability to form a phage. Induction of a phage eliminates action of a repressor, is shown by the activation of repressed genes of a prophase leading to its cutting from a chromosome of a cell with the help the website-siyetsi-ficheskoy of a recombination with participation, the proteins coded by genes of a phage. In a condition of an autonomous derepressi-rovanny ring molecule, as well as at a lytic cycle of development of a phage, DNA is replicated at first in a ring form, and later from - an intermediate replicative form linear molecules, characteristic of virions, are formed. Replication comes in two naprav-

lines from the point of the beginning of replication fixed on a ring molecule with participation of the proteins coded by two genes of a phage under difficult control of its systems of positive and negative regulation. The lytic cycle of development comes to the end within 50 min. with assembly of phage particles, a lysis of a cell and release apprx. 100 virions forming muddy negative colonies on a lawn of bacteria owing to their lysogenization (see Gratsia a method). Disturbance of borders of cutting a prophase can lead to partial substitution of its DNA the adjoining bacterial genes with formation of the defective phage particles which are carrying out specific transduction (see). At a phage a lambda numerous various mutations are known, with the help to-rykh in its genome the St. 40 genes are mapped. Allocate 4 basic groups of genes: recombinations,

DNA replications, the regulatory and determining structural components of a phage and genes of a lysis of a cell. The first three groups of genes function at an early stage of development of a phage, the last — on late. Extended deletsionny mutants with loss to 85% of a genome, but the kept replicons and mutants on a regulatory gene of N, function as typical plasmids (see), without integrating into a chromosome of a cell and without forming phage particles.

See also Bacteriophage.

Bibliography: D and to and r e in S. of and R about -

z and N about in M. N. Acellular system of packaging of DNA in a capsid of a phage I, Molek. genite., mikrobiol. and virusol., No. 8, page 12, 1983; The Phage a lambda, the lane with English, under the editorship of B. N. Ilyashenko, M., 1975; Heys U. Genetika of bacteria and bacteriophages, the lane with English, M., 1965; L e d e of b e of g E. M of Lysogenicity in E. coli K-12, Genetics, v. 36, p. 560, 1951. B. H. Ilyashenko.

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