DNA conformational transitions induced by supercoiling control transcription in chromatin.

Regulation of transcription in eukaryotes is considered in the light of recent findings demonstrating the presence of negative and positive superhelical tension in chromatin. This tension induces conformational transitions in DNA duplex. Particularly, the transition into A-form renders DNA accessible and waylaying for initiation of transcription producing RNA molecules long known to belong to the A-conformation.

[The expected nucleotide sequence of the human genome should be shortened about twofold].

The sizes of nucleotide sequences of chromosomes 21 and 22 of the human genome established in three independent laboratories were compared with the sizes expected from the accurately determined contribution of these chromosomes to the genome mass. It was found that the expected haploid mass of the genome is about twofold smaller than the lowest of the figures published. This strongly contradicts the current notions about the genome size.

A model of self-maintenance of in vivo malignant growth not dependent on tumour type or origin: syndrome of everlasting wound healing.

The common mechanism of permanent growth maintenance in all types of malignant tumours is proposed. According to the model, the main event, stimulating tumour growth is the stochastic but permanent death of a proportion of tumour cells as a result of inherent genetic instability of tumour cell genome (chromosome fragility). Dead cells trigger the complex and multicomponent process of wound healing, manifesting in stimulation of cell proliferation, angiogenesis, cell migration and other events.

[A common link in the mechanism of the self-maintenance of malignant growth: the syndrome of the nonhealing wound].

A general principle of the maintenance of malignant growth in all types of tumors has been formulated. According to this principle, stochastic but continuous death of some tumor cells due to the inherent genetic instability of their genome (fragility of chromosomes) is the main event stimulating tumor growth. The dead cells trigger a complex multicomponent process of wound healing expressed as further proliferation of living tumor cells, angiogenesis, stimulation of cell migration, and other events.

Experimental evidence for the binemic structure of human chromosomes.

A binemic model of eukaryotyc chromosome was tested using PCR-amplification of some unique genes in individual sperm cells or in human DNA diluted to 1/2 of the DNA amount of a haploid cell. According to the model, all the hereditary information, including all the unique genes, is represented twice in the haploid genome. Backing up of information enhances reliability of the genome by several orders of magnitude.

Relationship of histone acetylation to DNA topology and transcription.

An autonomously replicating plasmid constructed from bovine papiloma virus (BPV) and pBR322 was stably maintained as a nuclear episome in a mouse cell culture. Addition to a cell culture of sodium butyrate (5 mM) induced an increase in plasmid DNA supercoiling of 3-5 turns, an increase in acetylation of cellular histones, and a decrease in plasmid transcription by 2- to 4-fold. After withdrawal of butyrate, DNA supercoiling began to fluctuate in a wave-like manner with an amplitude of up to 3 turns and a period of 3-4 h.

High rotational mobility of DNA in animal cells and its modulation by histone acetylation.

DNA rotational mobility in a bovine papilloma virus (BPV)-based minichromosome, autonomously replicating in mouse cells, was studied using topoisomer analysis in temperature shift experiments. It was found that in live cells the average number of topological turns increased by six in the course of temperature shift through a range of 37 degrees C. This comprised approximately 85% of the total potential mobility of naked plasmid DNA.

A. E. Braunstein Plenary Lecture. Nuclear skeleton, DNA domains and control of replication and transcription.

Chromosomal DNA is organized in loops or domains of about 100 kb. Their ends seem to be attached to special protein skeletal structures. The DNA-attachment sites can be subdivided into permanent and transient types.

Inhibition of transcription in eukaryotic cells by X-irradiation: relation to the loss of topological constraint in closed DNA loops.

X irradiation was found to inhibit in vivo transcription in mammalian, yeast, insect and avian cells in a dose-dependent manner. Measurements of DNA nicking indicated that about one DNA single-strand break per estimated DNA loop (domain) length is sufficient to explain the effect. The inhibitory effect was partially reversed by post-irradiation incubation of cells.

Effect of X-ray induced DNA damage on DNAase I hypersensitivity of SV40 chromatin: relation to elastic torsional strain in DNA.

The effect of X-irradiation on DNAase I hypersensitivity of SV40 minichromosomes within nuclei or free in solution was investigated. The susceptibility of the specific DNA sites in the control region of minichromosomes to DNAase I decreased in a dose dependent manner after irradiation of isolated nuclei. On the other hand, the irradiation of minichromosomes extracted from nuclei in 0.

DNAaseI-hypersensitive minichromosomes of SV40 possess an elastic torsional strain in DNA.

Previously, we have shown that DNA in a small fraction (2-5%) of SV40 minichromosomes was torsionally strained and could be relaxed by treating minichromosomes with topoisomerase I. This fraction was enriched with endogeneous RNA polymerase II (Luchnik et al., 1982, EMBO J.

[Various novel properties of transcriptionally active mini-chromosomes of the SV40 virus].

The treatment of isolated SV40 mini-chromosomes by DNA-topoisomerase I leads to relaxation of DNA within a small fraction (2-5%) of mini-chromosomes strongly enriched in endogenous RNA-polymerase. The DNA supercoiling in the bulk of mini-chromosomes remained unchanged. The relaxable fraction proved to be specifically hypersensitive to DNAase I, but lost hypersensitivity after prior topoisomerase treatment.

[Phosphorylation of the nuclear matrix proteins of the liver and of Zajdela's hepatoma in the rat].

The rate of protein phosphorylation in isolated nuclear matrices from liver and Zajdela's hepatoma is very high, being even slightly higher than in isolated nuclei. This indicates that active protein kinases remain tightly bound to the nuclear matrix, since the areas of phosphorylation are the same. However, during isolation of the nuclear matrix from labeled nuclei in the absence of proteolysis and dephosphorylation inhibitors, most part of the label is eliminated from nuclear matrix proteins.

[Changes in DNA supercoiling during differentiation, aging and malignant transformation].

The data on changes in DNA supercoiling during cell differentiation, in vitro aging and SV40 virus-induced or spontaneous malignant transformation are discussed. The observed correlation between the level of cell proliferation and the density of DNA topological ("titratable superhelical") turns in the closed nuclear DNA loops, as well as the data on the effect of DNA supercoiling on transcription allow to suggest that the selective and co-ordinated switch in the transcription of genes involved in the control of cell proliferation may operate through total changes in the level of supercoiling of the closed nuclear DNA loops.

[Disorder of the repair of DNA double-stranded breaks in radiosensitive mutants of Saccharomyces cerevisiae yeasts].

DNA double-strand break repair and restoration of viability in X-irradiated diploid yeast cells homozygous for rad50, rad51, rad52, rad55 mutations were studies under conditions of keeping the cells in non-nutrient medium, after irradiation. All the cells were synchronized at the G1 stage of the cell cycle. In contrast to the wild-type yeast, this group of mutants are unable to repair DNA double-strand breaks and do not enhance viability, when kept in non-nutrient medium after irradiation.