The binding of all known linker histones, named H1a through H1e, including H1 0 and H1t, to a model chromatin complex based on a DNA fragment containing the mouse mammary tumor virus long terminal repeat promotor was systematically studied. As for the histone subtype H1b, we found a dissociation constant of 8 -16 nM to a single mononucleosome (210 base pairs), whereas the binding constant of all other subtypes varied between 2 and 4 nM. Most of the H1 histones, namely H1a, H1c, H1d/e, and H1 0 , completely aggregate polynucleosomes (1.3 kilobase pairs, 6 nucleosomes) at 270 -360 nM, corresponding to a molar ratio of six to eight H1 molecules per reconstituted nucleosome. To form aggregates with the histones H1t and H1b, however, greater amounts of protein were required. Furthermore, our results show that specific types of in vivo phosphorylation of the linker histone tails influence both the binding to mononucleosomes and the aggregation of polynucleosomes. S phase-specific phosphorylation with one to three phosphate groups at specific sites in the C terminus influences neither the binding to a mononucleosome nor the aggregation of polynucleosomes. In contrast, highly phosphorylated H1 histones with four to five phosphate groups in the C and N termini reveal a very high binding affinity to a mononucleosome but a low chromatin aggregation capability. These findings suggest that specific S phase or mitotic phosphorylation sites act independently and have distinct functional roles.H1 histones are a heterogeneous group of at least five subtypes with closely related but nonetheless different primary structures (1, 2). Two further H1 subtypes are known: the histone H1 0 , which is found in nonreplicative tissues (3, 4) and in rapidly proliferating cells (5), and the testis-specific histone variant H1t (6). The various linker histones containing a globular central region flanked by highly basic and hydrophilic C-and N-terminal tails (7,8) bind to the nucleosome and promote the organization of nucleosomes to a higher order structure (9, 10).There is evidence that histone H1 may interact differently with transcriptionally active and inactive regions of chromatin (11). Linker histones are also thought to modulate nucleosome position (12, 13) and to influence replication efficiency in vitro (14).The presence of this large number of various H1 histone subtypes and their possible posttranslational modifications, such as phosphorylation (15), make it very probable that H1 histones play numerous structural and functional roles in chromatin. Until now, no specific role for the various variants has been established although Kaludov et al. (16) showed that the mouse histone H1b binds preferentially to a regulatory sequence within a mouse H3.2 replication-dependent histone gene. Previous analysis of the structural role of H1 histones demonstrated that three subfractions of H1 histones differ in their effectiveness in condensing DNA fibers into ordered aggregates (17) and that histone subtype H1t, compared with other subtypes, dif...

Ischemic stroke (IS) outcome predictors include clinical features, biochemical parameters and some risk factors. The relations between two main players in the ischemic brain, MMPs and HMGB1, were estimated in the plasma of ischemic stroke patients stratified according to the Glasgow Outcome Scale and the Oxfordshire Community Stroke Project classification. IS patients exhibited higher plasma concentration of MMP-9 and the inflammatory cytokine HMGB1 compared with healthy controls. A full-blown correlation between MMP-9 activation and increased plasma MMP-9 concentration was observed in case of IS patients. A similar activity of MMP-2 and MMP-12 was characteristic of healthy volunteers and IS patients. In patients with ischemic stroke increased plasma levels of MMP-9 and HMGB1 are associated with a poor functional outcome and are significantly correlated with each other (P=0.0054). We suggest that diagnostic benefits will be obtained if plasma HMGB1 levels are measured for IS patients in addition to MMP-9.

Arthrobacter species is of interest because of its high potential for bioremediation. Bacteria can detoxify chromium, by either reduction or accumulation inside the bacteria and/or absorption of chromium(VI) (CrVI) on their surface, and efflux pump. The possible pathway of Cr(VI) reduction by Arthrobacter oxydans isolated from Columbia basalt rocks at a US DOE highly contaminated site (USA) has been considered in the present study. FTIR absorption spectroscopy showed that these bacteria reduce Cr(VI). In the present study the threshold Cr(VI) nontoxic concentration (35 microg/mL) for A. oxydans growing in liquid medium was estimated. Complete uptake of this concentration was achieved in about 10 days after chromium addition into the medium. At this concentration an increase in the protein isolated from the cell wall of A. oxydans was observed. This increased protein predominated independently of the growth phase at which Cr(VI) was added. Thermal analysis was used to identify any influence of Cr(VI) on the DNP complex of A. oxydans. According to the data obtained it can be supposed that Cr(VI) reduction predominantly occurs on the bacterial surface and that cell wall represents a permeable barrier for these bacteria at the non-toxic chromium action.

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The aim of this study is to establish antioxidant indicators of chromium toxicity in fetal human lung fibroblasts (HLF). The results obtained corroborate and develop our earlier observation of low-dose and long-term action of Cr(VI) on human cells in culture. In the case of a nontoxic chromium dose, temporary oxidative stress is overcome by increased activity of the antioxidant system with correlation to cell cycle re-entry. The toxic concentrations misbalance the cell antioxidant defense systems and cause irreversible growth arrest and massive cell death by apoptosis. Sub-toxicity is defined as toxicity stretched in time. The activity of GPx (glutathione peroxidase) is proposed as a biomarker of oxidative stress caused by Cr(VI), and the GR (glutathione reductase) inhibition is considered as a marker of the toxicity developed under the complex Cr(VI) action. In HLF cells the glutathione dependent defense system is the first system destroyed in response to toxic chromium action. Only the balance between SOD (superoxide dismutase) and H(2)O(2) degrading enzymes (catalase and GPx), should play an important role in the fate of a cell, not individual enzymes.

The changes in glutathione-dependent cycle enzymes and catalase activities under Cr(VI)-induced oxidative stress were investigated in two distinct cell lines: L-41-human epithelial-like cells and HLF-fetal human diploid lung fibroblasts, which differ in tissue origin, proliferation, and antioxidant enzymes activities. The chromium concentrations from 1 to 5 μM cause nontoxic effects and activate antioxidant enzymes to overcome oxidative stress. In spite of some differences in the endogenous antioxidant activities, both cell lines reveal the same range of toxic concentrations (20-30 μM). The irreversible inhibition of glutathione-dependent antioxidant enzymes develops under toxic concentrations and serves as a marker of toxicity. The endogenous antioxidant activity influences time-dependent expression of Cr(VI) toxicity and the dynamics of antioxidant enzymes activity under nontoxic conditions. The cell antioxidant defense system is an important marker of the cell adaptive capacity under nontoxic and toxic conditions.

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