PubMed Health⌕ Search

Biomedical subjects

V A Lantsov

Publications and source records attributed to V A Lantsov.

18 recordsLinked to original sources
PubMed1990

[Frequency of recombination exchanges in Escherichia coli K-12: genetic determinants controlling this frequency].

RecF, recQ, ruv, recJ and recN genes of so called RecF pathway of recombination appear to be not silent on the RecBCD pathway also. These genes are responsible for the frequency of recombination exchanges per unit length of DNA. The list: recF::Kmr greater than recQ::Tn3 greater than ruv54 greater than recJ::Tn9 demonstrated the efficiency of inhibition of recombination exchanges by these mutations. The recN262 mutation gives a feeble contrary effect. It slightly increases the frequency of recombination exchanges.

Escherichia coli↗
PubMed1990

[Comparative analysis of the structure and function of recA genes from Serratia marcescens Sb and Escherichia coli K-12].

Nucleotide sequence of the 1276 bp fragment of Serratia marcescens DNA coding for the recASM gene has been determined. This structure was shown to contain an ORF corresponding to a protein with molecular weight of 37766 D. Comparative analysis of the regulatory part of recASM and recAEC (Escherichia coli) demonstrated identity of "-35" and "-10" boxes for these genes and similarity of the SOS box and the enhancer sequences. A comparison of the amino acids sequences of RecASM, RecAEC and RecAPA (Pseudomonas aeruginosa) proteins revealed a great conservatism in the N-terminus and in some structural patches (alpha-helices and beta-sheets) of the RecA proteins predicted by the model of Blanar et al. In contrast, a strong variability of the C-terminus (for the last 25 amino acids, in particular) was revealed. A necessity for definite amino acids composition of the carboxy-terminal end is discussed.

Amino Acid Sequence↗
PubMed1987

[Transposition of the Tn5 and Tn10 elements and duplications in Escherichia coli K12 genome].

The kinetics of accumulation of resident transposon copies in a dividing population has been defined using a special experimental system. Analysis of the kinetics made it possible to estimate the probability of transposition for Tn5 as 2.5 X 10(-4) and for Tn10 as 2.3 X 10(-6) per cell per generation. Transposition of the composite elements does not depend on RecBC or RecF pathways of recombination. The fraction of the bacterial population with tandem duplications in the proA region of the genome is permanent for Escherichia coli. It is independent of the recombination pathways (RecBC of RecF) and the integrity of DNA polymerase I.

DNA Transposable Elements↗
PubMed1987

[DNA duplications detect the hidden transposition of the Tn5 element in the Escherichia coli K12 genome].

The frequency of Tn5 transposition localized in an arm of a tandem duplication was estimated as 1.3 X 10(-2) per cell per generation, two orders of magnitude higher than usual one. Approximately thirty per cent of all transpositions usually registered occur from the spontaneous duplications. The effect revealing latent transpositions is in good accordance with a conservative transposition model permitting some interesting predictions: 1. Composite transposons can be a reason for the double stranded cuts in DNA. 2. The transposition frequency in cis for composite elements seems to be many times higher than in trans. 3. Partially transpositions in cis can be recA dependent. 4. The estimation of Tn5 transposition in cis presented in the paper is a minimal one.

Chromosome Mapping↗
PubMed1987

[Composite transposons Tn5 and Tn10 in Escherichia coli K12: precise excision and recombination].

The number of exconjugants having the transposon Tn5 excised precisely during the crosses of the Escherichia coli proA::Tn5 donor with the recipients F- rec+ or F- recA441 (tif) was 20-30 times higher for the crosses involving the latter recipient. The high recombinogenic activity is characteristic of the tif recipient. Precise excision from a tandem duplication is more efficient than from nonduplicated region of the genome. It is four orders higher, if a transposon is localized in an arm of a duplication. The effect is recA-dependent. The presented data permit us to suggest the participation of RecA protein (its synaptic function) in the formation of the intermediate "stem-loop" structure. The latter is predicted by the three mechanisms of transposon excision: "slippage", "correctional" and "recombinational". The latter two mechanisms were formulated in the paper. The experimental proof of the postexcision transposition presented in the paper, is a good support to the version of "recombinational" excision.

Conjugation, Genetic↗
PubMed1986

[The genetic Rec system of homologous recombination in Escherichia coli].

A review of modern data on genetic and biochemical bases of the Rec system is presented. Taking into consideration the final result of recombination, that is the preferential way of integration of donor DNA into recipient chromosome, it is proposed to distinguish three main pathways of homologous recombination RecBC (recF- recipient genotype), RecF (recBC- sbcB- sbcC-) and SOS. A recBC nuclease unwinds a donor linear DNA duplex to create the 3'-single-stranded end which was shown to be responsible for the initiation of recombination with the help of RecA protein. As a result, integration of single- and double-stranded donor fragments into recipient chromosome takes place in full accordance with the Meselson-Radding model. The peculiarity of the RecF pathway is its ability to promote recombination between two DNA closed ring structures. The SOS way is characterized by frequent single-stranded DNA exchanges. Both pathways are interconnected. The SOS way is regarded here as an extreme situation of the RecF one.

Escherichia coli↗
PubMed1985

[Bacterial RecA protein: a biochemical, genetic and physicochemical analysis].

A review of the role of evolutionary significant bacterial RecA protein in the cell is presented. The topics discussed are: elementary properties of the protein; its main functions in the cell (recombination and SOS-response); the formation, dissociation and regulation of the activated RecA protein complex and its cofactors, including the single-stranded DNA binding protein (SSB); functional domains in the recA gene structure; formation of RecA protein complex with single- and double-stranded DNA; RecA-like proteins in different microorganisms.

Adenosine Triphosphate↗
PubMed1977

[Bacterial recombination].

The most perspective trends in studying the mechanisms of genetic exchanges in bacteria are discussed. They are the following. 1. Comparison of the recombination stages in various biological phenomena such as transformation, transduction (generalized), conjugation (common and single-stranded) and transfection. 2. Characterization of genetic determinants and basic enzymes of the recombination process in Rec-systems of different bacteria. 3. Determination of some peculiar features of the intragenic recombination and finding a possible approach to their research. 4. Analysis of some plastic properties of the DNA structure and their application to the modern ideas in the formulation of a molecular mechanism of genetic recombination.

Bacillus subtilis↗
PubMed1977

[Single-stranded conjugation in Escherichia coli K-12: characteristics of the formation of a heterogenous progeny].

During a single-stranded conjugation donor DNA, being a single-stranded form, takes part in the process of recombination. That is why a heteroduplex DNA must be an intermediate product of the recombination. The heteroduplex can be partially corrected as it was supposed for genetic transformation. The division of such a corrected heteroduplex gives the heterogenous progeny of exoconjugants. And this "correctional" heterogeneity must possess two following properties: 1) the mixed progeny must consist of only two recombinational genotypes; 2) the heterogeneity must be marker-specific. The experimental support to both predictions was obtained by the method of clonal analysis of conjugational merozygotes.

Conjugation, Genetic↗
PubMed1977

[Mechanism of genetic recombination in bacterial conjugation. VIII. The heterogeneity of the progeny of exconjugants].

It is shown on several examples that the heterogeneity of recombinant clones after conjugation is independent on the conditions of primary selection (i.e. on the yield of primary clones). Therefore the prediction of the model of autonomously multiplying donor fragments is not confirmed by experimental data. Two additional characteristics of heterogeneity are introduced. The statistical distribution of merozygotes according to segregation time is measured. It is an exponential curve with a relaxation time approximately coinsident with the third cell division. A liner function is found for the dependence of heterogeneity on the distance between the selective and non-selective markers. The highest value for non-linked markers is about 15%. Alternative models for the explanation of the heterogeneity of exconjugants are discussed.

Bacteria↗
PubMed1976

[Mechanism of genetic recombination during bacterial recombination. VI. Single-stranded conjugation].

The mutation BT43 in the dnaB gene inhibits conjugational DNA synthesis in the recipient cell at 42 degrees C. Since only one DNA strand is transferred from the donor to the recipient in these conditions, this single strand is integrated into the recipient chromosone. This is characterized by a high increase of recombination frequency per length unit, an effect well known in the case of transformation. This peculiar genetic process is proposed to be called "single stranded conjugation". It is more efficient in recipient cells recB-recC-sbcB-lacking two main degrading enzymes, exonucleases I and V. The proof of single strandedness was given by means of clonal analysis in a special experiment. The transfer of the selected marker into the thermosensitive recipient took place at 37 degrees C and the transfer of the non-selected marker -- at 42 degrees C. Thhe progeny of one merozygote must be mixed i.e. consist of cells with both alleles of the non-selected marker. This was confirmed by experimental data.

Conjugation, Genetic↗
PubMed1975

[Mechanism of conjugation in Escherichia coli K-12. IV. Conjugation in conditions of phenotypic suppression of gene dnaB mutation].

The thermosensitive mutation BT43 in the gene dnaB is a missence mutation affecting the vegetative and conjugational DNA synthesis. By means of the increase of ionic strength (NaCl concentration) in the medium the functional activity of the dnaB product is partially restored in non-permissive conditions. In these conditions a rescue of recombinant yield is observed. But the mechanism of recombination is switched from one-stranded to double-stranded. This is demonstrated by the alteration of the degree of linkage of genetically close markers.

DNA, Bacterial↗
PubMedDate not supplied

[Evidence for Campbell's mechanism for fine excision of Tn9 type transposons in Escherichia coli K12].

The plasmid-transposon Tn9-322 was constructed by inverted transposition from the pBR322::Tn9 plasmid. The precise excision of the Tn9-322 transposon from the proB gene site can proceed by the Campbell's model. This fact was demonstrated by appearance of the plasmid-transposons after their precise excision. They contain two IS1 elements flanking a short direct repeat of the target DNA. The recombinational mechanism of precise excision of Tn9 type transposons seems not to be alternative but looks as an additional one to a well-known slippage mechanism proved for Tn5 and Tn10.

Base Sequence↗