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V V Vel'kov

Publications and source records attributed to V V Vel'kov.

12 recordsLinked to original sources
PubMed1983

[Instability of recombinant molecules].

The regions and mechanisms of recombinant DNAs instability are reviewed, in particular, the mechanisms of the replication instability expressed as elimination of recombinant DNA from cells and the mechanisms of structural instability revealed as spontaneous alteration of the chemical structure of these DNAs. The replication instability is subdivided into that induced by ineffective replication systems, and that induced by disturbances in the process of correct partitioning of the plasmids between dividing cells. The structural instability is subdivided into topological one occurring due to formation in the hybrid plasmids of the anomalous elements of the secondary structure-"loops", the regulatory instability caused by nonbalanced transcription streams and metabolic instability induced because of the protein superproduction which is energy capacious and not necessary for normal cell growth.

Base Sequence↗
PubMed1982

[Gene amplification in prokaryote and eukaryote systems].

The studied cases of gene amplification in bacteriophages, bacteria, yeasts, Drosophila, animal viruses and animal cells are reviewed. It is suggested that gene amplification is the mechanism universal for all classes of organisms and necessary for: 1) rendering the needed overhigh level of gene expression provided that the efficiency of the given gene transcription reaches in maximum (adaptive amplification), 2) preferential genome replication in case the efficiency of replication initiation reaches its maximum (competitive amplification), 3) rendering the essential stable DNA-protein interaction, if this interaction is damaged by DNA deletion (compensatory amplification). Molecular mechanisms for gene amplifications are: a) multiple sequential gene duplications, b) differential overreplication, excision, extrareplication and reintegration.

Animals↗
PubMed1981

[Instability of hybrid plasmids containing Drosophila melanogaster DNA in rec+ and rec- Escherichia coli K-12 strains].

The stability of hybrid plasmids, constructed on the basis of vector pCV20(AprTcr) and containing HindIII fragments of Drosophila melanogaster DNA (pDm6, pDm9) and PstI fragments of D. melanogaster DNA (pDm39, pDm187, pDm189) was studied. After the transformation of E. coli HB101 recA and Escherichia coli 802 rec+ and selection to Tcr (pDm6, pDm9), or to Apr (pDm39, pDm189, pDm187) 0.04--9% of clones with reduced resistance to Tc or Ap was detected. The hybrid plasmids are more stable in rec-, but not in rec+ strain, the stability depends of the nature of cloned DNA, and on the site of vector DNA in which foreign genes are cloned. Restriction endonuclease analysis revealed that all plasmids of the clones with reduced Tcr or Apr lost the inserted DNA and the excision of foreign DNA occurred precisely in the sites of cloning. We suggest that the genome of the hybrid plasmid in the region of foreign insertion has a conformation which allows the bringing together the ends of cloned DNA with the following excision of the foreign genes.

Animals↗
PubMedDate not supplied

[New insights into the molecular mechanisms of evolution: stress increases genetic diversity].

The mechanisms of stress-induced mutagenesis in prokaryotes and realization of reserved (preaccumulated) genetic variation in eukaryotes are considered. In prokaryotes, replication becomes error-prone in stress because of the induction of the SOS response and the inactivation of the mismatch repair system; stress also increases the transposition rate and the efficiency of interspecific gene transfer. In eukaryotes, chaperone HSP90, which restores the native folding of mutant proteins (e.g., signal transduction and morphogenetic proteins) in normal conditions, fails to do so in stress, which leads to abrupt expression of multiple mutations earlier reserved in the corresponding genes. The role of these mechanisms in the evolution of prokaryotes and eukaryotes is discussed.

Adaptation, Physiological↗
PubMedDate not supplied

[The selection and properties of Penicillium verruculosum mutants with enhanced production of cellulases and xylanases].

The paper describes three Penicillium verruculosum 28K mutants with about threefold enhanced production of five industrially important carbohydrases. The two-stage fermentation process that we developed provided a further two- to threefold increase in the production of carbohydrases. Physiological and biochemical studies showed that the synthesis of all five carbohydrases is inducible. Carboxymethylcellulase, xylanase, and beta-glucanase are synthesized under a common regulatory control, as is evident from the concurrent increase in the synthesis of these enzymes in the presence of microcrystalline cellulose. The synthesis of avicelase and beta-glucosidase is evidently induced by other cellulose- and hemicellulose-containing compounds present in the fermentation medium and, hence, is regulated independently of the three aforementioned enzymes.

Cellulase↗
PubMedDate not supplied

[Study of the stability of hybrid plasmids replicating in Saccharomyces cerevisiae due to DNA fragments from polyoma virus].

Hybrid plasmid pSP97 carrying the entire genome of polyoma virus (PY), inserted into bacterial vector psV3, transforms yeast cells with the frequency 1 x 10(-2). Plasmid pSP97 is capable of autonomous replication in S. cerevisiae, while its structure remains unaltered, the stability of hybrid plasmid in transformants is 44%--100%. Plasmid pSP155 consisting of Ori-containing DNA segment from polyoma, pBR322 and yeast gene arg4, transforms yeast cells with the frequency 5 x 10(-3), the stability of plasmid in transformants is 23%--29%. Two types of plasmids were isolated from transformants: one was identical to SP155, while the another differed structurally and phenotypically from SP155. Plasmids pSP113 and pSP114, in addition to pBR322 and yeast gene arg4, contain a viral DNA segment that encodes genes from small and middle T-antigens. These plasmids transform yeast cells with low frequency (2 x 10(-4), 3 x 10(-5)), the stability of plasmids in yeast transformants is 100%. However, hybrid plasmids identical to pSP113 were isolated from transformants. Structural rearrangements have been observed in pSP114, which carries the arg4 gene in reversed orientation compared to pSP113.

Chromosome Mapping↗
PubMedDate not supplied

[Biochemical response of recombinant Hansenula polymorpha strains to oversynthesis of homologous dioxyacetone kinase and bacterial beta-galactosidase].

Changes in the activities of key enzymes responsible for utilization of methanol by recombinant strains of methylotrophic yeasts H. polymorpha R22-2B and H. polymorpha LAC-56 grown in a chemostat are described. The strain R22-2B displaying a high activity of dioxyacetone kinase had also a high activity of formaldehyde dehydrogenase, which increased the rate of dissimilation of formaldehyde. There was a decrease in ATP concentration in the strain LAC-56 oversynthesizing beta-galactosidase from Escherichia coli; this effect decreased the rate of assimilation of formaldehyde.

Adenosine Triphosphate↗