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

We have investigated the effects of mixed Na+: Mg2+ ionic solutions on the stability of the nonspecific lac repressor-DNA complex. The effects of Mg2+ are simply interpreted in terms of its role as a competitor (with repressor) for DNA sites. From these studies, the binding constant of the Mg-DNA complex can be determined as a function of the concentration of Na+. We have used this information to interpret the data of Riggs and collaborators (Riggs, A.D., et al. (1970), J. Mol. Biol. 48, 67-83; 53, 401-417) on the ion dependence of the repressor-operator interaction. We find that there are approximately 70% as many ionic interactions in the repressor-operator complex as in the nonspecific complex. Our best estimate is that 8 +/- 1 ion pairs are formed. We calculate that the release of counterions in the formation of the specific complex contributes approximately 40% of the favorable free energy change in the association reaction under in vivo ionic conditions. Implications of these findings for the control of the lac operon and for the molecular relationship between the specific and nonspecific complexes are considered.
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PMID:Interpretation of monovalent and divalent cation effects on the lac repressor-operator interaction. 91 90

An endogenous Ca2+, Mg2+-dependent factor of enzymic nature (apparently an endonuclease) digests a part of chromatin in the rat liver nuclei producing DNA fragments of an uniform size. After 60 min of incubation at 15 degrees C and pH 7.50 in the presence of 5 mM MgCl2 and 2 mM CaCl2 87-93% of the total chromatin becomes soluble. The insoluble chromatin however contains 70-85% of the in vivo newly synthesized RNA. In regenerating liver the proportion of the insoluble residual chromatin increases while the radioactivity of the newly synthesized DNA in this fraction is highest. Residual chromatin can be solubilized by ultrasonic treatment only. The Ca2+, Mg2+-dependent dissolving factor is not present either in brain or in PMN leucocyte nuclei.
Mol Biol (Mosk)
PMID:[Solubilization of chromatin by an endogenous enzymic Ca2+, Mg2+-dependent factor. Activity of residual chromatin]. 105 86

Dense gels of E. coli 70 S ribosomes, their 50 S subunits, CM-like particles, RNP strands and their fragments, 38 S particles obtained from RNP strand folding upon addition of Mg2+ ions, and of unoriented salt-free and free rRNA sodium and magnesium salts were studied by X-ray diffraction. It was shown that under dense gel conditions RNA molecules contained in ribosomes unfolded by desalting, like all other particles considered here, have helical regions. Under these conditions free desalted RNA has no helical regions. Experimental data on X-ray scattering at medium angles were compared with the diffraction curves calculated for homogeneous prolate and oblate ellipsoids, for various ellipsoids containing a dense region or an internal cavity, and for ellipsoids containing internal periodic regions. The results indicate that the internal structure of the 50 S ribosome is periodic, i. e., its components form a periodic lattice. The lattice spacings are approximately 42 and 28 A with a 0.8g/g dry weight sample water content. When the 50 S particle water content drops below 0.2 g/g dry weight the periodic structure is disrupted. This disruption is reversible. It was shown that CM-like particles at high ionic strenght (2 M LiCl) have approximately the same internal periodicity as the 50 S particles, but in contrast they lose this periodicity at low ionic strength (10-2M tris-HCl and 5-10-3 M MgCl2).
Mol Biol 1975 Jan
PMID:An x-ray diffraction study of ribosome structure. 109 99

The interaction of the oligonucleotides ApApA, ApApU and ApApC with polyribouridylic acid and of hexariboinosinic acid with and without phosphate near the 3'-end with polyribocytidylic acid was studied by the method of equilibrium gel filtration through Sephadexes. The free energy, the energy and entropy of the complexing were calculated from isotherms of the adsorption of the oligonucleotides on the polynucleotides in relation to the composition of the oligonucleotides and the concentration of magnesium ions in the buffer. It was shown that in the case of the interaction of ApApA and ApApC with poly(U) a perfect triple complex is formed, while in the case of the interaction of ApApU with poly(U) the noncomplementary base is partially displaced from the complex. The free energy of the interaction of neighboring oligonucleotides in a complex with polynucleotides is from --1000 to --3000 cal/mole depending on the type of the complex. It was shown that after the interaction of hexainosinic acid with poly(C) a double complex is formed. The free energy of the interaction of neighboring oligonucleotides in this complex is formed. The free energy of the interaction of neighboring oligonucleotides in this complex is about --1200 cal/mole. Magnesium ions have a different effect on the formation of triple and double complexes in the interaction of oligonucleotides with polynucleotides.
Mol Biol 1975 Jan
PMID:A study of the interaction of oligonucleotides with polynucleotides by the method of equilibrium gel filtration. The effect of magnesium ions and the composition of the oligonucleotides on the stability of the complex. 112 8

Free polyribosomes, isolated from liver, spleen and pancreas of the rat, were suspended in a medium at 0.5 mM Mg2+ and analyzed in the analytical ultracentrifuge. The percentage of run-off ribosomes, distinguised by a sedimentation coefficient below 77S was calculated from centrifugal experiments. The amount of run-off ribosomes differed in the various tissues of the rat but was not influenced by fasting overnight.
Mol Biol Rep 1975 Oct
PMID:Run-off ribosomes in liver, spleen and pancreas of the rat. 119 6

A few examples of incorrect interactions between aminoacyl-tRNA-synthetases and tRNAs extracted from the same organism have already been demonstrated. These interactions can lead, in most cases, to incorrect aminoacylations. The lack of specificity of the aminoacyl-tRNA suggests that incorrect interactions could be a general phenomenon. The aim of this study is to check whether incorrect interactions are a general feature, i.e. whether every aminoacyl-tTNA-synthetase is able to interact with homologous non-cognate tRNAs. In that case, it is interesting to know whether a given aminoacyl-tRNA-synthetase is able to recognize any tRNA or only a particular group of tRNAs. The existence of such groups would lead to the concept of tRNA families. For that, we estimated the affinities of non-cognate homologous tRNA species for yeast valyl-tRNA-synthetase by using competition experiments. The measured affinities varied, in standard aminoacylation conditions, between 1:100 to 1:1000 of that of the non-cognate tRNA. In the absence of Mg2+ ions or in the presence of low concentration of this cation, the affinities were higher and could reach 1:3 of the affinity of the cognate tRNA. On the other hand, we determined the inhibitory effect of a high concentration of tRNAVal toward the aminoacylation of tRNAs specific for 13 amino acids. In order to compare the effects, we determined approximate Km/Ki values. These values ranged from 0.07 for methionyl tRNA synthetase to 0.002 for leucyl tRNA synthetase. For some aminoacyl-tRNA-synthetases, the inhibition was too low to be detected by this technique. Two conclusions arise from this study. First, it seems that non-specific recognitions are quite a general phenomenon. Secondly, if one classifies tTNAs according to their affinities for valyl-tRNA-synthetase, it does not appear any well cut group of tRNAs. This result is not conflicting with the fact that on the basis of aminoacylation criteria several authors have found tRNA and aminoacyl-tRNA-synthetase families since we have already shown that discrimination depends rather on the maximal velocity of the reaction than on the affinity between the tRNA and the aminoacyl-tRNA-synthetases. Finally, the non-existence of clear-cut recognition families of tRNAs casts some doubts on the approach consisting in the characterisation of recognition sites of the tRNAs by the aminoacyl-tRNA-synthetases by comparing the sequences of tRNAs which are amonoacylated by a given aminoacyl-tRNA-synthetase.
Mol Biol (Mosk)
PMID:[Recognition between tRNAs and aminoacyl-tRNA-synthetases of different specificities]. 121 72

The incorporation of 32P into well washed human erythrocyte membranes was studied in a medium containing [gamma-32P]ATP, Mg2+, and EGTA. Following phosphorylation, the membranes were completely solubilized in 1% sodium dodecyl sulfate and subjected to gel electrophoresis in dodecyl sulfate polyacrylamide. A large incorporation of radioactivity was observed in a band which migrated faster than component 7 (nomenclature of T. L. Steck, (1972), J. Mol. Biol. 66, 295) but slower than the bromophenol blue tracking dye, and did not stain with Coomassie Blue. Isolation of this band by preparative gel electrophoresis revealed that 41% of the radioactivity was associated with a 32P-labeled polypeptide. This polypeptide was further purified by gel chromatography on Sephadex LH-20 in chloroform-methanol-HCl, and Bio-Gel A 1.5m in dodecyl sulfate. Its amino acid composition is characterized by a high content of acidic residues. The calculated minimal molecular weight is 15084. Based upon the recovery of amino acids, the polypeptide fraction comprises at least 1.8% by weight of the total erythrocyte membrane proteins. An apparent molecular weight of 15000 was estimated by gel chromatography in dodecyl sulfate, while a range of 14000-16000 was estimated by electrophoresis in dodecyl sulfate polyacrylamide. The state of phosphorylation of this peptide may reflect a physiological function in the intact red cell.
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PMID:Isolation of a 32P-labeled polypeptide of low molecular weight from phosphorylated human erythrocyte membranes. 124 9

The RNase P cleavage reaction was studied as a function of the number of base-pairs in the acceptor-stem and/or T-stem of a natural tRNA precursor, the tRNA(Tyr)Su3 precursor. Our data suggest that the location of the Escherichia coli RNase P cleavage site does not depend merely on the lengths of the acceptor-stem and T-stem as previously suggested. Surprisingly, we find that precursors with only four base-pairs in the acceptor-stem are cleaved by M1 RNA and by holoenzyme. Furthermore, we show that both disruption of base-pairing, and alteration of the nucleotide sequence (without disruption of base-pairing) proximal to the cleavage site result in aberrant cleavage. Thus, the identity of the nucleotides near the cleavage site is important for recognition of the cleavage site rather than base-pairing. The important nucleotides are those at positions -2, -1, +1, +72, +73 and +74. We propose that the nucleotide at position +1 functions as a guiding nucleotide. These results raise the possibility that Mg2+ binding near the cleavage site is dependent on the identity of the nucleotides at these positions. In addition, we show that disruption of base-pairing in the acceptor-stem affects both Michaelis-Menten constants, Km and kcat.
J Mol Biol 1992 Oct 20
PMID:Several regions of a tRNA precursor determine the Escherichia coli RNase P cleavage site. 127 79

The ability of cations to modulate the binding of the sigma 1 receptor-selective ligand (+)-[3H]pentazocine to guinea pig cerebellum was investigated. Di- and trivalent cations biphasically inhibited (+)-[3H]pentazocine binding, revealing multiple affinity states. The rank order of potency of these cations (based on the high affinity component of inhibition) was Zn2+ > Co2+ >> La3+ = Ni2+ = Cd2+ = Mn2+ = Gd2+ > Ba2+ = Sr2+ >> Mg2+ > Ca2+. The inhibition of 1,3-[3H]di(2-tolyl)guanidine binding to the sigma 2 receptor by these cations differed qualitatively and quantitatively from their effects on (+)-[3H]pentazocine binding. Although monovalent cations decreased the Kd for (+)-[3H]pentazocine binding, divalent cations split (+)-[3H]pentazocine binding into low and high affinity components. The Bmax of the high affinity component decreased with increasing divalent cation concentrations. Both mono- and divalent cations significantly reduced the rate of association of (+)-[3H]pentazocine with the sigma 1 receptor without altering the dissociation rate. (+)-[3H]Pentazocine binding was not altered by guanine nucleotides or by treatment with cholera or pertussis toxins. However, nonselective cation channel blockers (cinnarizine, hydroxyzine, prenylamine, amiodarone, and proadifen) potently inhibited (+)-[3H]pentazocine binding. These results indicate that physiologically relevant concentrations of divalent cations allosterically modulate (+)-[3H]pentazocine binding to the sigma 1 receptor, to reveal multiple affinity states. These sites do not represent sigma 1 to sigma 2 subtype interconversion or ternary complex formation with guanine nucleotide-binding proteins. However, the rank order of cation potency and the inhibition of binding by cation channel blockers is consistent with a potential role for sigma receptors as constituents of cation channels.
Mol Pharmacol 1992 Nov
PMID:Modulation of (+)-[3H]pentazocine binding to guinea pig cerebellum by divalent cations. 127 78

In order to study the conductances of the Sarcoplasmic Reticulum (SR) membrane, microsomal fractions from cardiac SR were isolated by differential and sucrose gradient centrifugations and fused into planar lipid bilayers (PLB) made of phospholipids. Using either KCl or K-gluconate solutions, a large conducting K+ selective channel was characterized by its ohmic conductance (152 pS in 150 mM K+), and the presence of short and long lasting subconducting states. Its open probability Po increased with depolarizing voltages, thus supporting the idea that this channel might allow counter-charge movements of monovalent cations during rapid SR Ca2+ release. An heterogeneity in the kinetic behavior of this channel would suggest that the cardiac SR K+ channels might be regulated by cytoplasmic, luminal, or intra SR membrane biochemical mechanisms. Since the behavior was not modified by variations of [Ca2+] nor by the addition of soluble metabolites such as ATP, GTP, cAMP, cGMP, nor by phosphorylation conditions on both sides of the PLB, a specific interaction with a SR membrane component is postulated. Another cation selective channel was studied in asymmetric Ca2+, Ba2+ or Mg(2+)-HEPES buffers. This channel displayed large conductance values for the above divalent cations 90, 100, and 40 pS, respectively. This channel was activated by microM Ca2+ while its Ca2+ sensitivity was potentiated by millimolar ATP. However Mg2+ and calmodulin modulated its gating behavior. Ca2+ releasing drugs such as caffeine and ryanodine increased its Po. All these features are characteristics of the SR Ca2+ release channel. The ryanodine receptor which has been purified and reconstituted into PLB, may form a cation selective pathway.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Cell Biochem 1992 Sep 08
PMID:Reconstitution and regulation of cation-selective channels from cardiac sarcoplasmic reticulum. 128 Dec 62


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