[Genetic predisposition factors for multiple sclerosis (based on the data from genotyping patients of the Russian ethnic group)]. / Faktory geneticheskoi predraspolozhennosti k rasseiannomu sklerozu (po dannym genotipirovaniia bol'nykh russkoi étnicheskoi gruppy).

Patients' genotyping of Russian ethnic group with multiple sclerosis (MS) was performed for the first time in two loci of the main complex of histocompatibility: in DR HLA class II (gene DRB1) and in the locus of tumor necrosis factors (TNF). There was no difference in the incidence of alleles groups which correlated with some specificity of DR. Meanwhile TNF-a1 and TNF-a9 alleles were encountered significantly more frequently in patients and TNF-a7 in control group. When all the patients and controls examined were divided into groups in dependence on combination of DR and TNF it was found that relations observed between MS and TNF-a7 and TNF-a9 alleles were displayed much more in individuals which carried alleles of gene DRB1, corresponding to DR15 specificity. These are alleles which are known as the main risk factor of MS in Caucasians. The patients with "protective" TNF-a7 allele were characterized by more favorable course of the disease. Thus highly significant genetic markers were revealed for the first time in region of TNF genes which were associated with increased or decreased risk of MS development at least in Russian ethnic group. There was also possibility of their interaction with group of DR15 alleles of DRB1 gene. One of the markers revealed (TNF-a7) occurred to be bound both with decreased risk of MS and with favorable clinical course, which was observed for genetic markers of MS for the first time. Manifestation of one or another property of TNF-a7 marker depends on the presence of alleles of DRB1 gene which corresponds to DR15 specificity.

Primary organization of nucleosomal core particles is invariable in repressed and active nuclei from animal, plant and yeast cells.

A refined map for the linear arrangement of histones along DNA in nucleosomal core particles has been determined by DNA-protein crosslinking. On one strand of 145-bp core DNA, histones are aligned in the following order: (5') H2B25,35-H455,65-H375,85,95/H488-H2B105,11 5-H2A118-H3135,145/H2A145 (3') (the subscripts give approximate distance in nucleotides of the main histone contacts from the 5'-end). Hence, the histone tetramer (H3,H4)2 and two dimers (H2A-H2B) are arranged on double-stranded core DNA in a symmetrical and rather autonomous way: H2A/H3-(H2A-H2B)-(H3,H4)2-(H2B-H2A)-H3/H2A. The primary organization was found to be very similar in core particles isolated from repressed nuclei of sea urchin sperm and chicken erythrocytes, from active in replication and transcription nuclei of Drosophila embryos and yeast and from somatic cells of lily. These data show that (i) the core structure is highly conserved in evolution and (ii) the overall inactivation of chromatin does not affect the arrangement of histones along DNA and thus does not seem to be regulated on this level of the core structure.

DNA supercoiling by core histone fractions and protamine.

The nuclear extract isolated from late Drosophila melanogaster embryos has Mg2+-dependent DNA topoisomerase 1 and nuclease activities. The extract facilitates the closed circular duplex DNA supercoiling in the presence of calf histone fractions H2A, H2B, H3 and H4, and fish protamine but not HI histone.

[Unfolding of nucleosome cores induced by chemical acetylation of histones]. / Razvorachivanie korovykh nukleosom, vyzvannoe khimicheskim atsetilirovaniem gistonov.

Relative accessibility of nucleosomal histones to acetic anhydride during acetylation has been studied as a function of concentration, pH and ionic strength of the solution using high-resolution gel-electrophoresis. It was shown that about 80% of lysine residues in nucleosomal histones and 100% of the same residues in histone complexes without DNA in 2 M NaCl are accessible to the modification, which is proved by the localization of the majority of lysine residues in nucleosomes near the surface of the histone octamer, by their participation in ionic interactions with DNA and, probably, in histone-histone contacts. Gel-electrophoretic experiments with nucleosomes and studies of the histone resistance to mild trypsinolysis indicated that neither nucleosomes themselves nor histone octamers are affected even though 50% of lysine residues in histones have been acetylated. The process of acetylation is accompanied by the growing tendency of histones to participate in mild trypsinolysis and by a gradual decline in electrophoretic mobility and in the value of the sedimentation constant. The circular dichroism spectra and the microscopic appearance of nucleosomes are also markedly changed. These results suggest that a gradual unfolding of nucleosomes occurs when 5 or more lysine residues in the nucleosomal histones have been acetylated.

[Isolation, some properties and heterogeneous nature of DNA-topoisomerase (relaxing enzyme) from Ehrlich ascites carcinoma cells]. / Vydelenie, nekotorye svoistva i priroda geterogennosti DNK-topoizomerazy (relaksiruiushchego fermenta) iz kletok astsitnoi kartsinomy Erlikha.

DNA-topoisomerase catalyzing the conversion of a superhelical circular covalently closed DNA molecule into a super-helix free circular molecule, was isolated from mouse Ehrlich ascites carcinoma cells and purified 209-fold. The optimal conditions for the action and stability of the enzyme were elaborated. Using polyacrylamide gel electrophoresis under non-denaturating conditions as well as in the presence of Na-DS the heterogeneity of purified DNA-topoisomerase was established. This heterogeneity implies the presence of three active forms of the enzyme with Mr of 97 000, 81 000 and 69 000, respectively. Using one-dimensional fingerprint method and limited proteolysis with Staphylococcus aureus protease, it was demonstrated that the low molecular weight enzyme forms are products of limited proteolysis of the highest molecular weight form of DNA-topoisomerase.

[Complexes of histone H1 with supercoiled DNA]. / Issledovanie kompleksov gistona H1 s superspiral'noi DNK.

The action of DNA topoisomerase I on the complexes of supercoiled DNA (DNA I) with histone H1 and other histones was studied at different ionic conditions and histone/DNA ratios. In the presence of 0.15 M NaCl at histone H1/DNA ratios lower than 0.25 (w/w) the relaxation of DNA I is not inhibited. Raising of H1/DNA I ratio up to 0.7 is followed by significant inhibition of DNA I relaxation. At fixed H1/DNA I ratio maximal inhibition is detected at 0.25 M NaCl. At NaCl concentrations lower than 0.1 M and higher than 0.3 M increasing of DNA I relaxation in the presence of H1 was observed. Electron microscopic studies show that increase of ionic strength or H1/DNA I ratio causes more dense packing of DNA molecules in the H1.DNA complexes. Changes in the structure of complexes agree with the increase of DNA I relaxation inhibition in these conditions. DNA I relaxation inhibition by H1 is drastically decreased by iodination of tyrosine 72 residue in the globular part of H1 molecule. Individual core histones inhibit DNA I relaxation at much higher histone/DNA ratios and show different dependence of inhibition on ionic strength. The results are discussed in terms of the possible role of H1 in chromatin condensation-decondensation.

[Drosophila melanogaster embryo factor capable of supercoiling circular covalently closed DNA in the presence of core histones H2a, H2b, H3, H4 or protamine]. / Superspiralizatsiia kol'tsevoi kovalentno zamknytoi DNK v prisutstvii gistonov H2, H2b, H3, H4 ili protamina i ekstrakta iz embrionov Drosophila melanogaster.

The Mg2+-dependent factor capable of introducing the superhelical turns into circular closed DNA in the presence of core histones H2a, H2b, H3, H4 or protamine in solution at physiological conditions has been isolated from Drosophila melanogaster embryos. The factor does not work with histone H1, cytochrome c, poly-L-lysine or tetralysine. It is assumed that the factor is responsible for folding of core histones into nucleosomes.