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A N Rekesh

Publications and source records attributed to A N Rekesh.

16 recordsLinked to original sources
PubMed1991

A physiological role for DNA supercoiling in the anaerobic regulation of colicin gene expression.

The mechanism of anaerobic regulation of synthesis of colicins E1, E2, E3, K and D was studied. It was found that anaerobiosis significantly increases expression of the genes for colicins E1, E2, E3, K, and D. Experiments with novobiocin (a DNA gyrase inhibitor) showed that colicin synthesis in minicells and derepressed colicin synthesis in cells are dramatically reduced by relaxation of DNA supercoiling. A good correlation was observed between the levels of colicin synthesis and plasmid DNA supercoiling and the degree of aeration of the cultures. Thus, the regulation of colicin gene expression in response to a change in aeration appears to be mediated by environmentally induced variations in DNA supercoiling.

Anaerobiosis↗
PubMed1989

The effect of nonreceptor adsorption on the lethal action of colicin E1.

The survivability of Escherichia coli K12s cells has been studied after treatment with 125I-labeled colicin E1. It has been shown that for low amounts of adsorbed colicin the survivability follows single-hit kinetics. When the number of colicin molecules adsorbed exceeds approx. 50 per cell, deviation from single-hit kinetics occurs towards higher survivability. Colicin E1 adsorbed nonreceptorwise by the cell's surface has been shown to inhibit the lethal action of colicin E1 molecules adsorbed at specific receptors. This fact has been used in accounting for the elevated survivability of cells at high colicin doses. The functional significance of the phenomenon is discussed.

Adsorption↗
PubMed1987

[The nature of typhimuricin--a substance produced by Salmonella typhimurium LT2 and relation of its synthesis to the cryptic plasmid].

The effect of typhimuricin on Escherichia coli K12 cells and the properties of this substance produced by Salmonella typhimurium LT2 have been studied. The obtained data permit one to conclude that typhimuricin is similar to the aminoacid L-valine or the chemical very similar to it in properties. The synthesis of typhimuricin is not controlled by the cryptic plasmid present in Salmonella typhimurium LT2 cells. The experiments aimed at isolation of enterobacterial strains producing low molecular mass antibiotics--microcines have been done. It was found that the capability to produce macrocines is not widespread among the isolates of enterobacteria.

Bacteriocins↗
PubMed1977

[In vivo and in vitro studies of phage T4 lysozyme mRNA translation].

Translation of phage T4 lysozyme mRNA is studied in vivo and in vitro. Polyribosomes, carrying growing lysozyme polypeptides, are found to be homogenous enough and to contain 6 ribosomes. Complete molecules of phage lysozyme, which possess an enzymatic activity and are similar to the native enzyme in its electrophoretic mobility in polyacrylamide gel, have been synthetized in vitro on RNA isolated from phage-infected cells. The efficiency of RNA translation in cell-free system is discussed on the model of synthesis of functionally active individual protein.

Cell-Free System↗
PubMedDate not supplied

[Molecular mechanisms of regulating mammalian sex and problems of fractionating spermatozoa].

We present results of a study devoted to genetic determination and to the mechanism of primary sex differentiation in mammals. Progress is achieved in the mapping of a Y chromosome region necessary and sufficient for testis determination in man (TDF) and mouse (Tdy). We discuss a possible role in sex regulation of a recently described highly conservative locus from this region, ZFY (and similar loci within other chromosomes probably coding for Zn-binding proteins, transcription regulators) and H-Y antigen as well. We note that neither locus ZFY nor H-Y can play the role of TDF (Tdy) and that studies in this direction should be carried out. Numerous works on fractioning according to sex of spermatozoa of mammals including man are critically reviewed. Contradictory data exist in literature concerning the applicability of different approaches for this purpose: from fractioning based on different inherent mobility of different sex cells or gel-filtration, to the sorting in a flow cytometer equipped with a laser light source and a computer. However, in many cases the principle underlying this or that method of fractionation and determining the positive results, i.e. the statistically important shift of the sex ratio as compared with the initial sperm, remains unclear. It is stated that on the immunological and electrophoretic approaches might appear most promising for practical application, and in cattle-breeding as well. Modern procedures for sex testing and the fertility control of spermatozoa are also examined.

Animals↗
PubMedDate not supplied

[Spontaneous synthesis of colicin].

We studied regularities of the spontaneous synthesis of colicin E1 and its regulatory role in the survival of each cell and the population. For the first time, colicin from spontaneously induced cells was isolated and characterized, and the kinetics of its synthesis determined in a separate cell. It was stated that the time of colicin accumulation in an induced cell and the half-time period of a similar cell exceeds the period of cell doubling by 1.5 and 2 times, respectively. Spontaneously synthesized colicin was shown not to differ from the colicin synthesized by using inductors of the SOS-system of cell reparation. A conception was formulated of a biological system containing both colicinogenic cells with plasmids with encoded proteins of colicin, immunity and lysis on them and competitive plasmid-free cells sensitive or resistant to colicin. Environment dependent colicin synthesis in the system shown is regarded as regulator functioning according to the feed-back principle.

Chromatography, Affinity↗
PubMedDate not supplied

[The role of pulsed gel electrophoresis in the study of biological macromolecules].

We present modern conceptions concerning movement of biopolymer molecules in a gel under the action of static and pulsed electric fields, and we basically analyse some mostly used techniques of pulsed electrophoresis and the results yielded by using them. Pulsed procedures are shown to essentially widen the possibilities of analytical electrophoresis and electrophoretic transblotting are elaborated. Cameras and buffer systems used are the same as in classical methods involving the constant electric field. Promising results were collected while using sine-mode voltage in the constant and pulsed variants of electrophoresis. It is stated that the exceptionally wide application of pulsed methods in laboratory practice requires development of adequate theoretical conceptions concerning the movement of linear and globular polymers in gel under alternating field. In this connection the investigation of potentials of pulsed electrophoresis with inversions of field direction as the most simple and universal process of DNA division in a wide range of molecular masses and the use in electrophoretic techniques of sine-mode voltage obtained directly from the industrial circuit are most significant.

Biopolymers↗
PubMedDate not supplied

[The effect of supercoiling of DNA from colicinogenic plasmids on the expression of col, imm and lys genes].

The expression of colicin genes is controlled by the SOS-system (Lex A repressor) and the adenylate-cyclase system (cAMP-CAP complex). The effect of plasmid DNA supercoiling on the expression of the operons of colicins E1, E2, and E3 has been studied by using E. coli minicells. It has been shown for the colicin E1 operon that it is the promoter that is influenced by supercoiling: an increase in negative supercoiling elevates the expression and, vice versa, DNA relaxation reduces the expression. The effect of supercoiling on gene activity of the colicin E1 immunity protein has not been observed, which may be due to the specific orientation of this gene. With the two other colicins supercoiling affects the expression of all genes which constitute the operon. The regulation of the colicin operon expression has been confirmed to occur at three levels: by the LexA protein, by the cAMP-CAP complex, and by the plasmid DNA supercoiling.

Bacterial Proteins↗
PubMedDate not supplied

[Study of the regulation of colicin E1 and K synthesis].

Synthesis of colicins E1 and K and other plasmids was studied using DNA templates of corresponding plasmids in a cell-free system of coupled transcription and translation. Up to 15 plasmid-specific polypeptides differing by molecular weight were detected electrophoretically in conditions of complete denaturation. Samples of polypeptides related to plasmids ColE1 and ColK were similar in size. A complete or partial substitution of plasmid-free cell extracts by plasmid-containing cell extracts in a cell-free system leads to repression of the synthesis of colicins and some other proteins which is indicated by diminishing or complete disappearance of electrophoretic bands of corresponding polypeptides. The repression is relieved by addition of the recA gene protein into a cell-free system. Based on the obtained results, a conclusion is made that the repressors of colicin genes are not strictly specific and are, probably, coded by plasmids.

Bacteriocin Plasmids↗
PubMedDate not supplied

[Plasmid proteins inhibiting the activity of K and E1 colicins].

Plasmid proteins with m. w. of 14 000--15 000 were chromatographically isolated from lysates of E. coli cells containing plasmids ColK and ColE1. These proteins can reversibly inhibit the killing activity of K and E1 colicine and appear to be the immunity proteins of ColK and ColE1 plasmids and provide the defence of colicinogenic cells from their own colicin. The immunity protein of the ColK plasmid acts both upon K colicin and E1 colicin and vice versa. Unlike E2, E3 colicins or CloDF13 cloacin, K and E1 colicins are extracted from cells in a free state and not in a complex with the immunity protein.

Bacterial Proteins↗
PubMedDate not supplied

[Classical and pulsed gel electrophoresis of biopolymers. Theory and applications].

The work is devoted to the modern theory of gel electrophoresis in stationary and alternating electric fields, and it brings together results of numerous theoretical and experimental studies hitherto conducted. Main attention is drawn to the approximation definitions used in theory and to cases of divergences between theory and experimentation. Basic methods of gel electrophoresis and electrotransfer are principally analysed that appeared not long ago and showed to be greatly perspective. The resolution ability, advantages and disadvantages of pulsed methods are analysed, methods and instrumentation used in laboratory practice are described. Quantitative assessment of most important dependencies of applied significance are shown.

Biopolymers↗