Histones H2a, H2b, H3, and H4 form a tetrameric complex in solutions of high salt.

In 2 M NaCl, histones H2b, H2a, H3, and H4 form a heterotypic tetrameric complex made up of one chain of each histone. This complex has been analyzed by hydrodynamic techniques. It is indistinguishable from histones in chromatin by its resistance to trypsin, pattern of reactivity with 125I. and ability to form specific crosslinked products after treatment with formaldehyde. It is proposed that this complex is responsible for protecting the small DNA fragments produced by exhausting nuclease digestion of nuclei and that on the average two of these complexes protect the larger 180-200 base pair unit produced by partial treatment of nuclei with nuclease.     

Amide H/2H exchange reveals a mechanism of thrombin activation

Thrombin is a dual action serine protease in the blood clotting cascade. Similar to other clotting factors, thrombin is mainly present in the blood in a zymogen form, prothrombin. Although the two cleavage events required to activate thrombin are well-known, little is known about why the thrombin precursors are inactive proteases. Although prothrombin is much larger than thrombin, prethrombin-2, which contains all of the same amino acids as thrombin, but has not yet been cleaved between Arg320 and Ile321, remains inactive. Crystal structures of both prethrombin-2 and thrombin are available and show almost no differences in the active site conformations. Slight differences were, however, seen in the loops surrounding the active site, which are larger in thrombin than in most other trypsin-like proteases, and have been shown to be important for substrate specificity. To explore whether the dynamics of the active site loops were different in the various zymogen forms of thrombin, we employed amide H/(2)H exchange experiments to compare the exchange rates of regions of thrombin with the same regions of prothrombin, prethrombin-2, and meizothrombin. Many of the surface loops showed less exchange in the zymogen forms, including the large loop corresponding to anion binding exosite 1. Conversely, the autolysis loop and sodium-binding site exchanged more readily in the zymogen forms. Prothrombin and prethrombin-2 gave nearly identical results while meizothrombin in some regions more closely resembled active thrombin. Thus, cleavage of the Arg320-Ile321 peptide bond is the key to formation of the active enzyme, which involves increased dynamics of the substrate-binding loops and decreased dynamics of the catalytic site.     

H2, a temperate bacteriophage isolated from Bacillus amyloliquefaciens strain H

Bacillus amyloliquefaciens strain H is lysogenic for a large temperate phage we call H2. H2 has a polyhedral head 85 nm in diameter and a tail of about 17 x 434 nm. H2 lysogenizes Bacillus subtilis between the tyrA and metB genes, and gives specialized transduction of metB and, at lower frequencies, of ilvD and ilvA. The phage carries a thymidylate synthase gene and converts thymine auxotrophs of B. subtilis to prototrophy. The H2 genome is a linear DNA molecule about 129 kb in length. DNA extracted from phage particles grown in B. subtilis is not cut by the restriction endonucleases HaeIII, Fnu4HI, Bsp1286I, and BamHI; the latter enzyme is produced by B. amyloliquefaciens strain H. The prophage in lysogenic B. subtilis cells can be cut by these enzymes. We have isolated H2 mutants that carry the transposon Tn917, or a mutation resulting in clear-plaque morphology, or both.     

H3 and H4 histone cDNA sequences from Xenopus: a sequence comparison of H4 genes

Ovarian poly (A) + RNA from Xenopus laevis and Xenopus borealis was used to construct two cDNA libraries which were screened for histone sequences. cDNA clones to H4 mRNA were obtained from both species and an H3 cDNA clone from Xenopus laevis. The complete DNA sequences of these clones have been determined and are presented. These new sequences are compared with other H3 and H4 DNA sequences both in the coding and 3' noncoding regions. We find that there is considerable non-random codon usage in ten H4 genes. In addition there are some sequence similarities in the 3' noncoding regions of H3 and H4 genes.     

Acidification of the malaria parasite's digestive vacuole by a H+-ATPase and a H+-pyrophosphatase

As it grows within the human erythrocyte, the malaria parasite, Plasmodium falciparum, ingests the erythrocyte cytosol, depositing it via an endocytotic feeding mechanism in the "digestive vacuole," a specialized acidic organelle. The digestive vacuole is the site of hemoglobin degradation, the storage site for hemozoin (an inert biocrystal of toxic heme), the site of action of many antimalarial drugs, and the site of proteins known to be involved in antimalarial drug resistance. The acidic pH of this organelle is thought to play a critical role in its various functions; however, the mechanisms by which the pH within the vacuole is maintained are not well understood. In this study, we have used a combination of techniques to demonstrate the presence on the P. falciparum digestive vacuole membrane of two discrete H(+) pumping mechanisms, both capable of acidifying the vacuole interior. One is a V-type H(+)-ATPase, sensitive to concanamycin A and bafilomycin A(1). The other is a H(+)-pyrophosphatase, which was inhibited by NaF and showed a partial dependence on K(+). The operation of the H(+)-pyrophosphatase was dependent on the presence of a Mg(2+)-pyrophosphate complex, and kinetic experiments gave results consistent with free pyrophosphate acting as an inhibitor of the protein. The presence of the combination of a H(+)-ATPase and a H(+)-pyrophosphatase on the P. falciparum digestive vacuole is similar to the situation in the acidic tonoplasts (vacuoles) of plant cells.     

In vitro exchange of nucleosomal histones H2a and H2b

We have asked whether exogenous, radiolabeled histones can exchange with nucleosomal histones in an in vitro system. Using two different electrophoretic techniques, we were able to separate the histones contained in nucleosomes from those histones which were simply bound to the surface of the chromatin. Fluorography was used to determine which of the exogenous histones exchange with the nucleosomal histones. We observed substantial exchange of histones H1, H2a, and H2b when the chromatin and exogenous histones were incubated under approximately physiological conditions. We have also observed a small amount of exchange of H2a and H2b, as well as a substantial exchange of H1, from one chromatin fragment to another. Other conditions affecting the exchange of histones H2a and H2b are also reported.     

Identification of a dual histamine H1/H3 receptor ligand based on the H1 antagonist chlorpheniramine

Combining the first generation H(1) antihistamine chlorpheniramine (1) with H(3) ligands of the alkylamine type has led to the identification of compound 9d, a dual ligand of both the H(1) and H(3) receptors.     

Structure of a duck H3 variant histone gene: a H3 subtype with four cysteine residues

A duck recombinant DNA phage library was screened for H3 histone genes, and the sequence of a variant H3 gene, which appears not to be part of a histone gene cluster, has been determined. As derived from the nucleotide sequence, this gene codes for a 135-amino acid (aa) protein (as any other H3) and shows 10 aa substitutions compared with most published H3 structures. Six of these aa changes are based on one nucleotide (nt) substitutions in arginine codons. This results in three new histidines and, in addition to the highly conserved cysteine at position 110, three more cysteines are found in this H3 histone subtype.     

Factor H is a dermatan sulfate-binding protein: identification of a dermatan sulfate-mediated protease that cleaves factor H

Dermatan sulfate mediates the blood coagulation cascade by binding to heparin cofactor II and potentiating the antithrombin activity. In order to explore another function of dermatan sulfate, a dermatan sulfate affinity column was prepared from biotinylated dermatan sulfate and Streptavidin Sepharose. When human plasma was applied on the dermatan sulfate column, factor H was bound and cleaved. The cleavage products, a 30-kDa N-terminal fragment and a 120-kDa fragment, were eluted from the column with 500 mM NaCl and detected after Western blotting with anti-factor H. The bond between the tandem arginine residues in the sixth domain of factor H was cleaved. When purified factor H was applied on the column, the factor H was not cleaved and was recovered from the column as an intact 150-kDa fraction. The finding that dermatan sulfate-mediated cleavage of factor H was inhibited by (p-amidinophenyl) methanesulfonyl fluoride, but not N-ethylmaleimide or EDTA, indicates that a serine protease in the plasma was activated on the dermatan sulfate column and factor H was cleaved without intervention of the plasma protease inhibitors. Amidase activity was detected in the effluent from the dermatan sulfate column but was abolished by pretreatment of the plasma with dermatan sulfate. Therefore, dermatan sulfate participates in the activation of a protease as well as having the protease inhibitory action.     

H2S, a new neuromodulator

The formation of H2S from cyst(e)ine is catalyzed by three enzymes, cystathionine beta synthase, cystathionase, and 3-mercaptopyruvate sulfurtransferase. In the liver, kidney, enterocytes and vascular smooth muscle cells, H2S is principally synthesized by cystathionase. In contrast, it is synthesized by cystathionine beta synthase in the brain and partially by 3-mercaptopyruvate sulfurtransferase in cardiac tissue. H2S is catabolized, essentially in mitochondria by thiosulfate reductase. The sulfite generated is then oxidized to sulfate by sulfite oxidase. The amount of thiosulfate excreted in the urine is the best indicator of H2S biosynthesis, together with sulfhemoglobin determination in erythrocytes. H2S acts as a neuromodulator in the brain, increasing responses mediated by NMDA receptors, facilitating the induction of long-term potentialization in the hippocampus. H2S also acts as a vasodilator, acting directly on ATP-dependent potassium channels in vascular smooth muscle cells. The concentration of H2S is abnormally low in the brains of subjects with Alzheimer's disease, due to changes in the concentration of the physiological activator of cystathionine beta synthase. The overproduction of H2S described in subjects with Down's syndrome probably results from the overproduction of cystathionine beta synthase, as the gene encoding this protein is located on chromosome 21.     

H5 influenza,a global update

H5 influenza viruses have caused much alarm globally due to their high pathogenic potential. As yet we have not seen sustained spread of the virus amongst humans despite a high prevalence of the virus in avian populations. Nevertheless, isolated human cases of infection have demonstrated high mortality and there are substantial efforts being taken to monitor the evolution of the virus and to undertake preparedness activities. Here we review and discuss the evolution of the A/goose/Guangdong/1/96 (H5N1) virus with emphasis on recent events.     

Microbial biodegradation of a novel fluorotelomer alcohol, 1H,1H,2H,2H,8H,8H-perfluorododecanol, yields short fluorinated acids

The accumulation of perfluorooctanoic acid (PFOA) has been detected in wildlife, soil, and water. Further, 8:2 fluorotelomer alcohol (8:2 FTOH) is used for the industrial synthesis of other fluorotelomer compounds, surfactants, and polymeric materials; however, it was recently found to be a potential source of PFOA contamination in the environment. 1H,1H,2H,2H,8H,8H-perfluorododecanol (degradable telomer fluoroalcohol (DTFA)), which is a newly developed fluorotelomer, contains the –CH₂– group in the fluorinated carbon backbone, making it potentially degradable through biological reactions. In this study, we investigated the biodegradation of DTFA in a mixed bacterial culture obtained from activated sludge. Optimized quantitative liquid chromatography–mass spectrometry analysis of the predicted metabolites generated in the culture revealed accumulations of the transformation products from DTFA to 2H,2H,8H,8H-PFDoA and 2H,8H,8H-2-PFUDoA via multiple processes. Furthermore, the production of short fluorinated compounds, perfluorobutanoic acid, perfluoropentanoic acid, and perfluoropentanedioic acid, which are believed to have lower accumulation potential and toxicity toward organisms than PFOA, was determined.