Unstructured N Terminus of the RNA Polymerase II Subunit Rpb4 Contributes to the Interaction of Rpb4·Rpb7 Subcomplex with the Core RNA Polymerase II of Saccharomyces cerevisiae

Two subunits of eukaryotic RNA polymerase II, Rpb7 and Rpb4, form a subcomplex that has counterparts in RNA polymerases I and III. Although a medium resolution structure has been solved for the 12-subunit RNA polymerase II, the relative contributions of the contact regions between the subcomplex and the core polymerase and the consequences of disrupting them have not been studied in detail. We have identified mutations in the N-terminal ribonucleoprotein-like domain of Saccharomyces cerevisiae Rpb7 that affect its role in certain stress responses, such as growth at high temperature and sporulation. These mutations increase the dependence of Rpb7 on Rpb4 for interaction with the rest of the polymerase. Complementation analysis and RNA polymerase pulldown assays reveal that the Rpb4 center dot Rbp7 subcomplex associates with the rest of the core RNA polymerase II through two crucial interaction points: one at the N-terminal ribonucleoprotein-like domain of Rpb7 and the other at the partially ordered N-terminal region of Rpb4. These findings are in agreement with the crystal structure of the 12-subunit polymerase. We show here that the weak interaction predicted for the N-terminal region of Rpb4 with Rpb2 in the crystal structure actually plays a significant role in interaction of the subcomplex with the core in vivo. Our mutant analysis also suggests that Rpb7 plays an essential role in the cell through its ability to interact with the rest of the polymerase.

The generalized anomeric effect in the 1,3-thiazolidines: Evidence forboth sulphur and nitrogen as electron donors. Crystal structures of various N-acylthiazolidines including mercury(II) complexes. Possible relevance to penicillin action

Evidence for the generalized anomeric effect (GAE) in the N-acyl-1,3-thiazolidines, an important structural motif in the penicillins, was sought in the crystal structures of N-(4-nitrobenzoyl)-1,3-thiazolidine and its (2:1) complex with mercuric chloride, N-acetyl-2-phenyl-1,3-thiazolidine, and the (2:1) complex of N-benzoyl-1,3-thiazolidine with mercuric bromide. An inverse relationship was generally observed between the. C-2-N and C-2-S bond lengths of the thiazolidine ring, supporting the existence of the GAE. (Maximal bond length changes were similar to 0.04 angstrom for C-2-N-3, S-1-C-2, and similar to 0.08 angstrom for N-3-C-6.) Comparison with N-acylpyrrolidines and tetrahydrothiophenes indicates that both the nitrogen-to-sulphur and sulphur-to-nitrogen GAE's operate simultaneously in the 1,3-thiazolidines, the former being dominant. (This is analogous to the normal and exo-anomeric effects in pyranoses, and also leads to an interesting application of Baldwin's rules.) The nitrogen-to-sulphur GAE is generally enhanced in the mercury(II) complexes (presumably via coordination at the sulphur); a 'competition' between the GAE and the amide resonance of the N-acyl moiety is apparent. There is evidence for a 'push-pull' charge transfer between the thiazolidine moieties in the mercury(II) complexes, and for a 'back-donation' of charge from the bromine atoms to the thiazolidine moieties in the HgBr2 complex. (The sulphur atom appears to be sp(2) hybridised in the mercury(II) complexes, possibly for stereoelectronic reasons.) These results are apparently relevant to the mode of action of the penicillins. (c) 2006 Elsevier B.V. All rights reserved.

Effect of substitution on molecular conformation and packing features in a series of aryl substituted ethyl-6-methyl-4-phenyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carboxylates

The supramolecular structures of eight aryl protected ethyl-6-methyl-4-phenyl-2-thioxo-1,2,3,4 tetrahydropyrimidine-5-carboxyl ates were analyzed in order to understand the effect of variations in functional groups on molecular geometry, conformation and packing of molecules in the crystalline lattice. It is observed that the existence of a short intra-molecular C-H center dot center dot center dot pi interaction between the aromatic hydrogen of the aryl ring with the isolated double bond of the six-membered tetrahydropyrimidine ring is a key feature which imparts additional stability to the molecular conformation in the solid state. The compounds pack via the cooperative involvement of both N-H center dot center dot center dot S=C and N-H center dot center dot center dot O=C intermolecular dimers forming a sheet like structure. In addition, weak C-H center dot center dot center dot O and C-H center dot center dot center dot pi intermolecular interactions provide additional stability to the crystal packing.

Study of (Ba3MMWO9)-M-II-W-IV (M-II = Ca, Zn; M-IV = Ti, Zr) perovskite oxides: Competition between 3C and 6H perovskite structures

We describe an investigation of (Ba3MMWO9)-M-II-W-IV oxides for M-II = Ca, Zn, and other divalent metals and M-IV = Ti, Zr. In general, a 1:2-ordered 6H (hexagonal, P6(3)/mmc) perovskite structure is stabilized at high temperatures (1300 degrees C) for all of the (Ba3MTiWO9)-Ti-II oxides investigated. An intermediate phase possessing a partially ordered 1:1 double perovskite (3C) structure with the cation distribution, Ba-2(Zn2/3Ti1/3)(W2/3Ti1/3)O-6, is obtained at 1200 degrees C for Ba3ZnTiWO9. Sr substitution for Ba in the latter stabilizes the cubic 3C structure instead of the 6H structure. A metastable Ba3CaZrWO9 that adopts the 3C (cubic, Fm (3) over barm) structure has also been synthesized by a low-temperature metathesis route. Besides yielding several new perovskite oxides that may be useful as dielectric ceramics, the present investigation provides new insights into the complex interplay of crystal chemistry (tolerance factor) and chemical bonding (anion polarization and d(0)-induced distortion of metal-oxygen octahedra) in the stabilization of 6H versus 3C perovskite structures for the (Ba3MMWO9)-M-II-W-IV series.

Structural and spectral investigations on some new Ni(II) complexes of di-2-pyridyl ketone N(4)-phenylthiosemicarbazone

Ni(II)complexes(1-5)ofdi2pyridylketoneN(4)-phenylthiosemicarbazone (HL) have been synthesized and spectrochemically characterized. Elemental analyses revealed a NiL2 center dot 2H(2)O stoichiometry for compound 1. However, the single crystals isolated revealed a composition NiL, - 0.5(H,0)0.5(DMF). The compound crystallizes into a monoclinic lattice with the space group P-21/n. Complexes 2. 3 and 4 are observed to show a 1:1:1 ratio of metal: thioseicarbazone:gegenion, with the general formula NiLX center dot yH(2)O [X = NCS. Y = 2 for 2; X = Cl, Y = 3 for 3 and X = N-3, y = 4.5 for 4]. Compound 5 is a dimer with a metal:thiosemicarbazone:gegenion ratio of 2:2: 1. with the formula [Ni,L,(SO4)1 - 4H(2)O (c) 2007 Elsevier Ltd. All rights reserved.

Structural and spectral investigations on some new Ni(II) complexes of di-2-pyridyl ketone N(4)-phenylthiosemicarbazone

Ni(II) complexes (1-5) of di-2-pyridyl ketone N(4)-phenylthiosemicarbazone (HL) have been synthesized and spectrochemically characterized. Elemental analyses revealed a NiL2 center dot 2H(2)O stoichiometry for compound 1. However, the single crystals isolated revealed a composition NiL, - 0.5(H,0)0.5(DMF). The compound crystallizes into a monoclinic lattice with the space group P-21/n. Complexes 2. 3 and 4 are observed to show a 1:1:1 ratio of metal: thioseicarbazone:gegenion, with the general formula NiLX center dot yH(2)O [X = NCS. Y = 2 for 2; X = Cl, Y = 3 for 3 and X = N-3, y = 4.5 for 4]. Compound 5 is a dimer with a metal:thiosemicarbazone:gegenion ratio of 2:2: 1. with the formula [Ni,L,(SO4)1 - 4H(2)O (c) 2007 Elsevier Ltd. All rights reserved.

A novel fibre-coated sorbent for rapid removal of heavy metals from wastewater. Sorption of Zinc(II) from dilute aqueous solutions in the presence of high concentrations of common salts

The commercial acrylic fibre "Cashmilon" was partially hydrolyzed to convert a fraction of its nitrile (-CN) groups to carboxylic acid (-COOH) groups and then coated with polyethylenimine (PEI) resin and cross-linked with glutaraldehyde to produce a novel gel-coated fibrous sorbent with multiple functionalities of cationic, anionic and chelating types, and significantly faster sorption kinetics than bead-form sorbents. The sorption properties of the fibrous sorbent were measured using Zn(II) in aqueous solution as the sorbate to determine the effects of pH and the presence of common ions in the solution on the sorption capacity. The rate of sorption on the gel-coated fibre was measured in comparison with that on Amberlite IRA-68 weak-base resin beads, to demonstrate the marked difference between fibre and bead-form sorbents in their kinetic behaviour.

Study of (Ba3MMWO9)-M-II-W-IV (M-II = Ca, Zn; M-IV = Ti, Zr) perovskite oxides: Competition between 3C and 6H perovskite structures

We describe an investigation of (Ba3MMWO9)-M-II-W-IV oxides for M-II = Ca, Zn, and other divalent metals and M-IV = Ti, Zr. In general, a 1:2-ordered 6H (hexagonal, P6(3)/mmc) perovskite structure is stabilized at high temperatures (1300 degrees C) for all of the (Ba3MTiWO9)-Ti-II oxides investigated. An intermediate phase possessing a partially ordered 1:1 double perovskite (3C) structure with the cation distribution, Ba-2(Zn2/3Ti1/3)(W2/3Ti1/3)O-6, is obtained at 1200 degrees C for Ba3ZnTiWO9. Sr substitution for Ba in the latter stabilizes the cubic 3C structure instead of the 6H structure. A metastable Ba3CaZrWO9 that adopts the 3C (cubic, Fm (3) over barm) structure has also been synthesized by a low-temperature metathesis route. Besides yielding several new perovskite oxides that may be useful as dielectric ceramics, the present investigation provides new insights into the complex interplay of crystal chemistry (tolerance factor) and chemical bonding (anion polarization and d(0)-induced distortion of metal-oxygen octahedra) in the stabilization of 6H versus 3C perovskite structures for the (Ba3MMWO9)-M-II-W-IV series.

Mechanism of lectin-cell interactions: thermodynamic and kinetic analysis of the binding of winged bean acidic lectin (WBA II) to human erythrocytes

In order to identify the forces involved in the binding and to understand the mechanism involved, equilibrium and kinetic studies were performed on the binding of the winged bean acidic lectin to human erythrocytes. The magnitudes of delta S and delta H were positive and negative respectively, an observation differing markedly from the lectin-simple sugar interactions where delta S and delta H are generally negative. Analysis of the sign and magnitudes of these values indicate that ionic and hydrogen bonded interactions prevail over hydrophobic interactions resulting in net -ve delta H (-37.12 kJ.mol-1) and +ve delta S (14.4 J.mole-1 K-1 at 20 degrees C), thereby suggesting that this entropy driven reaction also reflects conformational changes in the lectin and/or the receptor. Presence of two kinds of receptors for WBA II on erythrocytes, as observed by equilibrium studies, is consistent with the biexponential dissociation rate constants (at 20 degrees C K1 = 1.67 x 10(-3) M-1 sec-1 and K2 = 11.1 x 10(-3) M-1 sec-1). These two rate constants differed by an order of magnitude accounting for the difference in the association constants of the two receptors of WBA II. However, the association process remains monoexponential suggesting no observable difference in the association rates of the lectin molecule with both the receptors, under the experimental conditions studied. The thermodynamic parameters calculated from kinetic data correlate well with those observed by equilibrium. A two-step binding mechanism is proposed based on the kinetic parameters for WBA II-receptor interaction

Indoleacetaldoxime hydro-lyase : II. Purification and properties

The purification and some properties of the enzyme indoleacetaldoxime hydrolyase (EC 4.2.1.29) from the fungus Gibberella fujikuroi, which dehydrates indoleacetaldoxime (IAOX) to indoleacetonitrile (IAN), are described. The enzyme activity in the fungus is present only under certain culture conditions. It is a soluble enzyme, has an optimum pH at 7, shows an energy of activation of —15,670 cal/mole, and has a Michaelis constant of 1.7 × 10−4 Image at 30 °. It appears to be specific for IAOX, and 1 mole of IAN is produced per mole of IAOX utilized. The enzyme is inhibited by a number of aldoximes of which phenylacetaldoxime (PAOX) is the most potent inhibitor. Inhibition by PAOX is competitive (Ki = 2.2 × 10−8 Image ). The enzyme is inhibited by SH reagents such as p-hydroxymercuribenzoate and N-ethylmaleimide, and by a number of SH compounds such as cysteine, β-mercaptoethanol, and 2,3-dimercaptopropanol (BAL). However, glutathione activates the enzyme. Metal chelating agents such as 8-OH-quinoline and diethyl dithiocarbamate inhibit the enzyme; the inhibition is partly reversed by ferric citrate. Ascorbic acid, and particularly dehydroascorbic acid (DHA), are good activators of the enzyme. Several other biological oxidants had either no action or had a slight effect. Potassium cyanide activates the enzyme at low concentration but inhibits at higher concentrations. Reduction of the enzyme with NaBH4 reduces activity, and the effect is partly reversed by pyridoxal phosphate and also by DHA. The above properties indicate that both an SH function and an oxidized function are required for activity.

Interrelations of micro-organisms and mulberry II. Phyllosphere microflora and nitrogen fixation in leaf and root surfaces

The mulberry leaves were shown to harbour substantial populations of bacteria, streptomycetes, yeasts, and moulds. Azotobacter and Beijerinckia were observed to contribute to nearly 5 to 10 per cent of the bacterial population. When grown in water culture under sterile conditions, Azotobacter inoculation on the leaf or root surface was found to increase plant growth, dry wt, and nitrogen content of the mulberry. The beneficial effect of Azotobacter was largely influenced by the presence of a carbon source in the plant nutrient solution. The root inoculation in comparison to leaf application was found to confer greater benefits to the growing plant. The presence of carbohydrates and amino acids in the leaf leachates of mulberry was shown. The mutual beneficial nature of the association of the plant and Azotobacter has been brought to light.

Metabolism of Plasmodium bergheistar, open: II. 32Pi incorporation into high-energy phosphates

Free parasites of Plasmodium berghei were found to incorporate labeled inorganic phosphate into high-energy phosphates by substrate linked and oxidative hosphorylation. But the parasites also appear to utilize the reserve ATP of the host cells when they are within the host cells which may indicate the dependence of the parasite on the host cells for provision of energy. This investigation formed part of the thesis submitted in 1965 for the doctoral degree at the Indian Institute of Science, Bangalore 12, India, and was supported in part by the Council of Scientific and Industrial Research, India.

A novel fibre-coated sorbent for rapid removal of heavy metals from wastewater. Sorption of Zinc(II) from dilute aqueous solutions in the presence of high concentrations of common salts

The commercial acrylic fibre "Cashmilon" was partially hydrolyzed to convert a fraction of its nitrile (-CN) groups to carboxylic acid (-COOH) groups and then coated with polyethylenimine (PEI) resin and cross-linked with glutaraldehyde to produce a novel gel-coated fibrous sorbent with multiple functionalities of cationic, anionic and chelating types, and significantly faster sorption kinetics than bead-form sorbents. The sorption properties of the fibrous sorbent were measured using Zn(II) in aqueous solution as the sorbate to determine the effects of pH and the presence of common ions in the solution on the sorption capacity. The rate of sorption on the gel-coated fibre was measured in comparison with that on Amberlite IRA-68 weak-base resin beads, to demonstrate the marked difference between fibre and bead-form sorbents in their kinetic behaviour.