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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mg(ClO4)2 induces the cooperative B-to-Z transition of poly[d(G-C)]; the salt concentration at the midpoint is 0.26 M. A comparison with previous data for NaCl, MgCl2 and NaClO4 (F.M. Pohl and T.M. Jovin, J. Mol. Biol. 67 (1972) 375) indicates that Mg(ClO4)2 is more effective than would be anticipated from the simple additive effects of the Mg2+ and ClO4- ions (the ionic strengths of the respective transition points are: NaCl, 2.4; MgCl2, 2.1; NaClO4, 1.8 and Mg(ClO4)2, 0.78). These results suggest the importance of specific interactions involving ClO4-, particularly in the presence of Mg2+. The B-Z transition of poly[d(G-C)] can be monitored spectroscopically via the large hyperchromic shift at 295 nm and the inversion in the CD spectrum. The reaction is fully reversible and can be fitted by a monoexponential function with half times varying between 8 and 150 min. The observed relaxation times are strongly dependent on the concentration of Mg(ClO4)2 with a distinct maximum at the transition point, in accordance with a concerted mechanism involving only the B and Z states. As the polymer assumes the Z conformation it progressively aggregates into a gel-like precipitate, which, however, redissolves rapidly upon lowering the salt concentration. The natural DNA from Micrococcus lysodeikticus which has a high GC content of 72% is also precipitated by Mg(ClO4)2 but we do not have direct spectroscopic evidence for the involvement of the Z conformation in this phenomenon. Neither calf thymus DNA (41% GC) nor poly[d(A-T)] (0% GC) aggregates under the same conditions.
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PMID:The B-Z conformational transition and aggregation of poly[d(G-C)] induced by moderate concentrations of Mg(CIO4)2. 360 35

Chromatin oligomers undergo a conformational change from a "10 nm" lower order structure at low concentration of salt to a "30 nm" higher order structure, with increasing NaCl or MgCl2 concentration. We have extended our previously reported hydrodynamic and light-scattering measurements of the folding of well-defined chicken erythrocyte chromatin fractions to include a study of the low angle X-ray scattering in solution. We show that it is feasible to identify the folding process with gradual compaction of a chain of freely joined filaments or a worm-like chain, within the limits of all the experimental data obtained. As the ionic strength is raised, the filament length of the oligomer, composed of Nz nucleosomes, decreases. At 75 mM-NaCl, the compacted model chains (Nz = 53) form structures that are, on average, cylindrically shaped with mean diameter 30 nm and length 104 nm. Helical symmetry need not be invoked in the modelling of the folding process and may, in particular, be difficult to establish in chicken erythrocyte chromatin, due to the non-uniform length of the DNA linker connecting the nucleosomes. Concerning the shape of the X-ray scattering profiles at various salt concentrations, it is possible in this way to rationalize two-slope cross-sectional plots, which have also been reported by other workers. Though this description represents a satisfactory conceptual presentation of a wealth of experimental data, it by no means represents a definitive solution to an exceedingly difficult problem.
J Mol Biol 1987 Feb 20
PMID:Transition of chromatin from the "10 nm" lower order structure, to the "30 nm" higher order structure as followed by small angle X-ray scattering. 361 90

Rat thymocytes were incubated for 2 min at 37 degrees C and the cells then broken by osmotic shock in 1.5 mM MgCl2 and the nuclei harvested. Treatment with 50 nM dexamethasone for 2 min resulted in about one third of nuclei showing abnormalities in appearance, in shape and density. This was not prevented by prior incubation for 10 min with actinomycin D and cycloheximide, but was when nuclei were isolated in the presence of anions larger than F- and Cl-, including I-, Br-, SO = 4 and citrate identical to. Subsequent addition of Cl- ion, however, resulted in development of abnormalities in steroid-treated nuclei. It is concluded that the steroid induces a mechanism resulting in influx of chloride ion leading to nuclear edema, which is not mediated by processes involving synthesis of macromolecules.
Mol Cell Biochem 1987 Jun
PMID:An effect of corticosteroids on thymocytes not mediated by macromolecule synthesis. 362 8

Are repressor binds to a single, partially symmetric, 21 base-pair operator site that is centered between the -10 and -35 regions of the Pant promoter. Protection and interference experiments show that Arc makes contacts with the operator on one side of the DNA helix. Although Arc is a small protein (53 residues/subunit), it makes contacts that are farther from the center of the operator than those made by many larger repressors. These extended contacts include the phosphate groups at the ends of the 21 base-pair site. Under standard conditions (pH 7.5, 100 mM-KCl, 3 mM-MgCl2, 22 degrees C) half-maximal operator binding is observed at an Arc concentration of 2.5 X 10(-9) M and the protein-DNA complex is very stable (t1/2 approximately equal to 80 min).
J Mol Biol 1987 May 20
PMID:Interaction of the bacteriophage P22 Arc repressor with operator DNA. 365 15

Electron microscopic observations of negatively stained myosin minifilaments in a solution containing 10 mM-citrate buffer (pH 8.0), 4 mM-MgCl2 reveal ordered assemblies. They reveal bundles of parallel minifilaments of about 330 nm in length, aggregated into periodic linear and hexagonal structures. These structures are formed by means of interaction between myosin heads, arranged at the ends of minifilament bundles. The addition of 1 mM-ATP to the above solution causes dissociation of minifilament bundles into individual minifilaments without preventing the latter from association into linear "end-to-end" assemblies. Phosphorylation of myosin light chains does not exert any noticeable effect on the structure of the ordered minifilament assemblies but significantly increases their quantity. The interaction between minifilaments observed by us should be taken into consideration in studies on the properties of myosin which make use of minifilament systems.
J Mol Biol 1987 Aug 05
PMID:Ordered assemblies of myosin minifilaments. 368 74

We have used flow linear dichroism (LD) and light scattering at 90 degrees to study the condensation of both DNA and calf thymus chromatin induced by spermine, triamines NH3+(CH2)iNH+(CH2)jNH3+, designated as much less than i, j much greater than: much less than 3, 4 much greater than (spermidine), much less than 3, 3 much greater than, much less than 2, 3 much greater than, much less than 2, 2 much greater than; the diamines putrescine and cadaverine and MgCl2. It is found that the different polyamines affected DNA and chromatin in a similar way. The degree of compaction of the chromatin fibers induced by spermine, triamines except much less than 2, 2 much greater than and Mg2+ has been found to be identical. The triamine much less than 2, 2 much greater than and the diamines studied do not condense either chromatin of DNA. Such a big difference in the action of the triamines indicates that not only the charge, but also the structure of the polycations are important for their interactions with DNA and chromatin. The stoichiometry of polyamine binding to chromatin at which condensation occurred is found to be 2 polyamine molecules per DNA helical turn. Polyamines are supposed to bind to the exposed sites of core DNA every 10 b.p. The extent of DNA phosphate neutralization by the histones is estimated to be about 55%. It has been shown that a mixture of mono- and multivalent cations affected DNA and chromatin condensation competitively and not synergistically, as claimed in a recent report by Sen and Crothers.
Mol Biol (Mosk)
PMID:[Interaction of polyamines with chromatin and DNA: formation of compact structures]. 368 84

The specificity and kinetics of rat sarcolemmal serotonin- and isoproterenol-stimulable adenylyl cyclases were studied. The stimulation of adenylyl cyclase by serotonin was less than that by isoproterenol and required low concentrations of ATP (0.1 mM), 10 microM GTP, and free Mg ion concentrations of 10-20 microM. The isoproterenol-stimulated activity was readily detectable over a much wider range of MgCl2 (1.0-5.0 mM) and ATP (0.1-3.0 mM). (+/-)-Oxprenolol and l(-)-propranolol inhibited isoproterenol stimulation with KB values of 6.3 X 10(-9) M and 1.9 X 10(-9) M, respectively. Interference by (+/-)-cyproheptadine, (+/-)-methysergide and d(+)-propranolol was not strictly competitive. However, these were much more potent inhibitors of serotonin stimulation than were oxprenolol and l-propranolol. The concentrations of antagonists producing 50% inhibition (IC50) of the maximal adenylyl cyclase stimulation by serotonin were compared to the IC50 obtained with isoproterenol; the ratios were 0.02 for oxprenolol, 0.50 for l-propranolol, 295 for d-propranolol, 2438 for cyproheptadine, 578 for methysergide and greater than 125,000 for lysergic acid diethylamide (LSD). These data indicate that rat skeletal muscle adenylyl is stimulated by discrete serotonergic and adrenergic receptors, and that there may be distinct conditions for optional stimulation.
Mol Cell Endocrinol 1986 Dec
PMID:Adrenergic and serotonergic regulation of skeletal muscle metabolism in the rat: specificity of the serotonin- and isoproterenol-stimulable adenylyl cyclase in sarcolemma. 380 7

Skeletal muscle actin labelled with pyrene was used to measure the critical concentration (Cc) for assembly in conditions designed to approximate the ionic environment in the cytoplasm. Under these conditions (0.1 M-KCl, 2 mM-MgCl2, 1.1 mM-ATP, 0.1 mM-CaCl2, 0.5 mM-ethyleneglycol-bis(beta-aminoethylether)N,N'-tetraacetic acid, 0.25 mM-2-mercaptoethanol, 20 mM-imidazol X HCl, pH 7.0), the steady-state Cc value was estimated to be 0.07 microM (3.0 micrograms/ml), and, consistent with previous observations, the Cc increased to 0.20 microM (8.7 micrograms/ml) in the presence of 10(-6) M-cytochalasin D, and to 1.10 microM (47 micrograms/ml) after conversion of ATP to ADP using hexokinase and glucose. Addition of inorganic phosphate (Pi) at concentrations up to 20 mM caused only a slight decrease in the steady-state Cc, but at 2 mM-Pi (a reasonable estimate of cytoplasmic concentrations) the increase in Cc due to cytochalasin D was abolished, and at higher Pi concentrations there was even a slight decrease. Increasing Pi concentrations also progressively reduced the steady-state Cc for ADP-actin close to that for ATP-actin. These results are consistent with an increased affinity of ADP-actin for the polymer in the presence of Pi. To determine whether these effects of Pi were simply mass action effects on hydrolysis of bound ATP by polymerized actin, the stoichiometry of ATP hydrolysis during actin assembly was estimated and found to be at unity within the limits of experimental error and to be unaffected by Pi up to 20 mM. In addition, actin depolymerized by removal of ATP using glucose and hexokinase rapidly reassembled after addition of 20 mM-Pi. These results are interpreted by a mechanism involving the formation of ADP-Pi-actin species and are discussed in relation to the phenomenon of treadmilling and the theory of dynamic instability, and the potential for their occurrence in cells.
J Mol Biol 1986 Sep 20
PMID:Cytoplasmic concentrations of inorganic phosphate affect the critical concentration for assembly of actin in the presence of cytochalasin D or ADP. 380 73

The process of chromatin compactization in nuclei at different concentrations of Mg2+ and/or Na+ ions has been investigated by analysis of chromatin cleavage pattern with DNase II. Nuclei of cells that differ in transcriptional activity and have different nucleosome DNA repeat length such as pigeon erythrocytes, rat cerebellum neurons and pigeon brain cortex neurons were studied. In the presence of 0-3 mM MgCl2 several compactization levels of nucleosomal fiber were revealed in chromatin of pigeon erythrocyte and rat cerebellum nuclei (nucleosome DNA repeat of 210 +/- 3 and 202 +/- 3 nucleotide pairs, respectively). Each of these levels are characterized by different types of periodical DNA fragmentation of chromatin with DNase II, namely formation of nucleosomal, "half-nucleosomal" (fragmentation via a 100 nucleotide pairs interval), and dinucleosomal periodicities. Similar compactization stages were shown also for isolated erythrocyte chromatin. In 0-3 mM MgCl2 chromatin of pigeon brain cortex neuron nuclei having nucleosome DNA repeat size 164 +/- 3 nucleotide pairs is cleaved with DNase II producing only a "half-nucleosomal" periodicity. A pattern of chromatin fragmentation was compared in the presence of Na+ and Mg2+ ions. In the presence of 10-100 mM NaCl or in 0.1-3 mM MgCl2 but in the presence of 50 mM NaCl erythrocyte chromatin condenses in nuclei forming a structure which is characterized only by a "half-nucleosomal" periodicity of fragmentation at DNase II action. Upon higher NaCl concentration (100-400 mM) in the presence of 3 mM MgCl2 a transition from dinucleosomal fragmentation to nucleosomal fragmentation of erythrocyte chromatin in nuclei with DNase I was observed.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Biol (Mosk)
PMID:[Structural organization of the nucleosomal chromatin fibril under various ionic conditions]. 380 10

The kinetics of formation and of dissociation of open complexes (RPo) between Escherichia coli RNA polymerase (R) and the lambda PR promoter (P) have been studied as a function of temperature in the physiological range using the nitrocellulose filter binding assay. The kinetic data provide further evidence for the mechanism R + P in equilibrium I1 in equilibrium I2 in equilibrium RPo, where I1 and I2 are kinetically distinguishable intermediate complexes at this promoter which do not accumulate under the reaction conditions investigated. The overall second-order association rate constant (ka) increases dramatically with increasing temperature, yielding a temperature-dependent activation energy in the range 20 kcal (near 37 degrees C) to 40 kcal (near 13 degrees C) (1 kcal = 4.184 kJ). Both isomerization steps (I1----I2 and I2----RPo) appear to be highly temperature dependent. Except at low temperatures (less than 13 degrees C) the step I1----I2, which we attribute to a conformational change in the polymerase with a large negative delta Cp degrees value, is rate-limiting at the reactant concentrations investigated and hence makes the dominant contribution to the apparent activation energy of the pseudo first-order association reaction. The subsequent step I2----RPo, which we attribute to DNA melting, has a higher activation energy (in excess of 100 kcal) but only becomes rate-limiting at low temperature (less than 13 degrees C). The initial binding step R + P in equilibrium I1 appears to be in equilibrium on the time-scale of the isomerization reactions under all conditions investigated; the equilibrium constant for this step is not a strong function of temperature and is approximately 10(7) M-1 under the standard ionic conditions of the assay (40 mM-Tris . HCl (pH 8.0), 10 mM-MgCl2, 0.12 M-KC1). The activation energy of the dissociation reaction becomes increasingly negative at low temperatures, ranging from approximately -9 kcal near 37 degrees C to -30 kcal near 13 degrees C. Thermodynamic (van't Hoff) enthalpies delta H degrees of open complex formation consequently are large and temperature-dependent, increasing from approximately 29 to 70 kcal as the temperature is reduced from 37 to 13 degrees C. The corresponding delta Cp degrees value is approximately -2.4 kcal/deg. We propose that this large negative delta Cp degrees value arises primarily from the burial of hydrophobic surface in the conformational change (I1 in equilibrium I2) in RNA polymerase in the key second step of the mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)
J Mol Biol 1985 Aug 05
PMID:Temperature dependence of the rate constants of the Escherichia coli RNA polymerase-lambda PR promoter interaction. Assignment of the kinetic steps corresponding to protein conformational change and DNA opening. 390 Apr 14


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