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William M. Balch 《Journal of phycology》1987,23(2):107-118
Transport of a nitrate analogue, 36Cl-ClO3−, was examined in two diatoms, Skeletonema costatum (Greve.) Cleve and Nitzschia closterium (Ehrenb) W. Sm. A dinoflagellate, Gonyaulax polyedra did not transport ClO3−. Transport of 36Cl-ClO3− by diatoms appeared to be active and showed saturation kinetics. The data were fitted by Michaelis-Menten equation at all but the lowest chlorate concentrations (where plots of S vs. v showed a slight concave bend). Affinity of cells for nitrate was considerably higher than for chlorate. The Ki for nitrate inhibition of chlorate transport was calculated assuming competitive inhibition. Light had little or no effect on chlorate transport. Pulse-chase experiments demonstrated that (1) ClO3− (hence NO3−) was stored in two intracellular compartments of equal size, (2) internal ClO3− was exchangeable with external ClO3− (rates of efflux and influx were measured), and (3) efflux of intracellular ClO3− showed transient states following a chase of ClO3− or NO3− which stabilized after 10–20 min. Transport of chlorate was a function of growth phase. 相似文献
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The origin of replication of the IncW plasmid pSa has been cloned and the function of this origin in Escherichia coli examined. A 1.9-kb region of DNA is required for efficient autonomous replication, and a 0.47-kb fragment within this region can initiate replication only in the presence of an autonomously replicating derivative of pSa. An Mr 35,000 protein (repA) is encoded adjacent to the origin and is required for efficient initiation of replication. The derivatives examined provide information suggesting a direct role of partition factors in plasmid replication and incompatibility. 相似文献
15.
Monos D Heliopoulos J Argyris E Cordopatis P Zompra A Kamoun M 《Journal of molecular recognition : JMR》2006,19(6):535-541
The cytoplasmic region of the CD2 receptor of lymphocytes contains proline-rich motifs, which are involved in T cell activation and interleukin-2 production. An intracellular CD2 binding protein, CD2BP2, interacts with two tandem PPPPGHR segments of the CD2 tail. CD2BP2 contains a GYF (glycine-tyrosine-phenylalanine) domain that confers binding to these proline-rich sequences. Monoclonal antibody 3E10 that was previously raised against a peptide containing the CD2 PPPPGHR segment reacts with the native CD2 molecule and spliceosomal Sm B/B' proteins. To identify the exact epitope on the CD2 peptide recognized by 3E10, a phage-displayed combinatorial peptide library was used. Analysis of the selected clones revealed that the mAb 3E10 binds preferentially to the motif PxxPPGxR. Experiments using amino acid substitutions with synthetic peptides confirmed the reactivity of mAb 3E10 with this motif. In addition, we show that several similarities exist between this motif and the CD2BP2-GFY recognition motif PPGxR/K. Binding of antibody 3E10 indicates some degree of degeneracy, which is consistent with its ability to recognize structurally related polyproline-arginine motifs found in intracellular proteins including Sm B/B' proteins and other RNA binding proteins. Thus, mAb 3E10 can be used to specifically identify a sub-class of proline-rich motifs, and as such can be used to study the potential role of these proline-rich sequences in mediating protein-protein interactions. 相似文献
16.
A modified pBR322 vector with improved properties for the cloning, recovery, and sequencing of blunt-ended DNA fragments 总被引:23,自引:0,他引:23
The construction of a plasmid vector which facilitates the cloning and recovery of blunt-ended DNA fragments is described. This plasmid, called pHP34, differs from pBR322 by a 10-bp insertion which introduces a unique SmaI site immediately flanked by two EcoRI sites. Blunt-ended DNA fragments cloned in the SmaI site can be recovered by digestion with EcoRI. Small cloned fragments can be chemically sequenced using a strategy which does not require their purification. The use of a plasmid related to pHP34 for in vitro mutagenesis by the insertion of a DNA linker fragment conferring an antibiotic resistance is also discussed. 相似文献
17.
Morett E Saab-Rincón G Olvera L Olvera M Flores H Grande R 《Journal of molecular biology》2008,376(3):839-853
Contemporary enzymes are highly efficient and selective catalysts. However, due to the intrinsically very reactive nature of active sites, gratuitous secondary reactions are practically unavoidable. Consequently, even the smallest cell, with its limited enzymatic repertoire, has the potential to carry out numerous additional, very likely inefficient, secondary reactions. If selectively advantageous, secondary reactions could be the basis for the evolution of new fully functional enzymes. Here, we investigated if Escherichia coli has cryptic enzymatic activities related to thiamin biosynthesis. We selected this pathway because this vitamin is essential, but the cell's requirements are very small. Therefore, enzymes with very low activity could complement the auxotrophy of strains deleted of some bona fide thiamin biosynthetic genes. By overexpressing the E. coli's protein repertoire, we selected yjbQ, a gene that complemented a strain deleted of the thiamin phosphate synthase (TPS)-coding gene thiE. In vitro studies confirmed TPS activity, and by directed evolution experiments, this activity was enhanced. Structurally oriented mutagenesis allowed us to identify the putative active site. Remote orthologs of YjbQ from Thermotoga, Sulfolobus, and Pyrococcus were cloned and also showed thiamin auxotrophy complementation, indicating that the cryptic TPS activity is a property of this protein family. Interestingly, the thiE- and yjbQ-coded TPSs are analog enzymes with no structural similarity, reflecting distinct evolutionary origin. These results support the hypothesis that the enzymatic repertoire of a cell such as E. coli has the potential to perform vast amounts of alternative reactions, which could be exploited to evolve novel or more efficient catalysts. 相似文献
18.
Evolution of the lipoprotein gene in the enterobacteriaceae. Cloning and DNA sequence of the lpp gene from Proteus mirabilis 总被引:3,自引:0,他引:3
We cloned the lipoprotein gene from Proteus mirabilis and determined its DNA sequence. Comparison with the lpp genes from Escherichia coli, Serratia marcescens, Erwinia amylovora and Morganella morganii revealed several unique features of the evolution of the lpp gene in the Enterobacteriaceae and enabled us to establish phylogenetic relationships between these bacteria. 相似文献
19.
Emission analysis of Tb3+‐and Sm3+‐ion‐doped (Li2O/Na2O/K2O) and (Li2O + Na2O/Li2O + K2O/K2O + Na2O)‐modified borosilicate glasses 下载免费PDF全文
B. Naveen Kumar Reddy S. Sailaja K. Thyagarajan Young Dahl Jho B. Sudhakar Reddy 《Luminescence》2018,33(3):486-494
Four series of borosilicate glasses modified by alkali oxides and doped with Tb3+ and Sm3+ ions were prepared using the conventional melt quenching technique, with the chemical composition 74.5B2O3 + 10SiO2 + 5MgO + R + 0.5(Tb2O3/Sm2O3) [where R = 10(Li2O /Na2O/K2O) for series A and C, and R = 5(Li2O + Na2O/Li2O + K2O/K2O + Na2O) for series B and D]. The X‐ray diffraction (XRD) patterns of all the prepared glasses indicate their amorphous nature. The spectroscopic properties of the prepared glasses were studied by optical absorption analysis, photoluminescence excitation (PLE) and photoluminescence (PL) analysis. A green emission corresponding to the 5D4 → 7F5 (543 nm) transition of the Tb3+ ions was registered under excitation at 379 nm for series A and B glasses. The emission spectra of the Sm3+ ions with the series C and D glasses showed strong reddish‐orange emission at 600 nm (4G5/2 →6H7/2) with an excitation wavelength λexci = 404 nm (6H5/2→4F7/2). Furthermore, the change in the luminescence intensity with the addition of an alkali oxide and combinations of these alkali oxides to borosilicate glasses doped with Tb3+ and Sm3+ ions was studied to optimize the potential alkali‐oxide‐modified borosilicate glass. 相似文献
20.
Yi-Shan Song 《Inorganica chimica acta》2005,358(1):191-195
A novel chain-like luminescent samarium coordination polymer {Sm3(C8H4O4)4(C12N2H8)2(NO3)}n (C8H4O4 = phthalate, C12N2H8 = 1,10-phenanthroline) has been assembled by hydrothermal process. The title complex crystallizes in the monoclinic system, space group P2(1)/c, with lattice parameters a = 22.56(3) Å, b = 11.155(15) Å, c = 20.32(3) Å, β = 96.70(2)°, V = 5078(12) Å3, F(000) = 2964, GOF = 0.857, R1 = 0.0358, wR2 = 0.0597, Z = 4. Samarium ions exhibit different coordination modes from each other and lead to the unexpected high asymmetrical structure. To our knowledge, it is the first example of lanthanide coordination polymers comprising the three asymmetrical central Sm3+ fragments. The photophysical properties have been studied with excitation and emission spectra. 相似文献