Nucleotide sequence of psbQ gene for 16-kDa protein of oxygen-evolving complex from Arabidopsis thaliana and regulation of its expression.

The psbQ gene encoding a 16-kDa polypeptide of the oxygen-evolving complex of photosystem II has been isolated from Arabidopsis thaliana and characterized. The gene consists of a 28 nucleotide long leader sequence, two introns and three exons encoding a 223-amino-acid precursor polypeptide. The first 75 amino acids act as a transit peptide for the translocation of the polypeptide into the thylakoid lumen. Expression studies show that the gene is light-inducible and expresses only in green tissues with high steady-state mRNA levels in leaves. Using this gene as a probe, restriction fragment length polymorphism between two ecotypes, Columbia and Estland, has also been detected.     

A physical and genetic map of the IncFI plasmid ColV2-K94

A restriction enzyme map of the IncFI plasmid ColV2-K94 was generated using EcoRI, BamHI, HindIII, and XhoI; the genetic features of this element were then mapped from previous heteroduplex studies.     

Crystallographic,morphological and photoluminescent investigations of Tb3+-doped YAlO3 perovskites for lighting applications

Terbium(III)-doped yttrium aluminate perovskite (YAP:xTb³⁺) (x = 0.01–0.08 mol) was synthesized using a simple gel-combustion method. Structural elucidations were performed using X-ray diffraction (XRD) and Rietveld analysis. Fourier-transform infrared spectral studies validated the efficient synthesis of designed doped samples. Transmission electron microscopic images showed the agglomerated irregular dimensions of the synthesized nanocrystalline materials. When excited at 251 nm, a strong emissive line attributed to ⁵D₄ → ⁷F₅ electronic transition was observed at 545 nm (green emission). The maximum luminescence was found at the optimized concentration (0.05 mol) of Tb³⁺ ions; this emission was quenched by dipolar–dipolar (d–d) interactions. Chromaticity (x and y) and correlated colour temperature parameters were obtained by analysing the emission profiles. Finally, the colour coordinates of nanophosphors were closer to the National Television Standards Committee green coordinates, which replicates their potency in the design and architecture of R-G-B-based white LEDs.     

Mechanism of racemization of amino acids by aspartate aminotransferase.

Aspartate aminotransferase (mitochondrial isoenzyme from chicken) has been found to racemize very slowly dicarboxylic amino acid substrates in the presence of their cognate oxo acids [Kochhar, S. & Christen, P. (1988) Eur. J. Biochem. 175, 433-438]. Tyrosine, phenylalanine and alanine are racemized at the same rate although they undergo the transamination reaction 3-5 orders of magnitude more slowly than the dicarboxylic substrates. Similarly, the truncated enzyme aspartate aminotransferase-(27/32-410) catalyzes the racemization at the same rate as the native enzyme, while its rate of transamination is decreased to 3% of that of the native enzyme. Apparently, the rate-limiting step in racemization is not immediately linked to the transamination cycle. Decreasing the water concentration in the reaction medium by adding methanol at 0 degrees C drastically reduces the rate of racemization without affecting the rate of transamination. On the basis of these and additional kinetic data and the model of the three-dimensional structure of the active site, we conclude that a water molecule is responsible for the protonation of C alpha of the coenzyme-substrate intermediate from the wrong side. The diffusion of the water molecule into the interior of the enzyme appears to be the rate-limiting step in aspartate-aminotransferase-catalyzed racemization.     

An active-site carboxyl group in liquefying α-amylase: specific chemical modification

Bacillus amyloliquefaciens -amylase activity is pH-dependent and the plot log (Vmax/Km) versus pH implicated a carboxyl group of aspartic acid/glutamic acid at the active site. Chemical modification of -amylase with EDC confirmed this view. Further, analysis of inactivation kinetics showed that modification of a single carboxyl group led to complete loss of the enzymic activity.     

Isopongaglabol and 6-methoxyisopongaglabol,two new hydroxyfuranoflavones from Pongamia glabra

Isopongaglabol and 6-methoxyisopongaglabol, two new hydroxyfuranoflavones, together with two furanoflavones 5-methoxyfurano(8,7-4″,5″)flavone and 5-methoxy-3′,4′-methylenedioxyfurano(8,7-4″,5″)flavone, two simple flavones, desmethoxykanugin and fisetin tetramethyl ether, a chromenoflavanone, ovalichromene B, two triterpenes, cycloart-23-ene-3β,25-diol and friedelin, and β-sitosterol-β-d-glucoside were isolated from the petrol and CHCl₃ extracts of the flowers of Pongamia glabra. The structures of isopongaglabol and 6-methoxyisopongaglabol have been established as 4′-hydroxyfurano(8,7-4″,5″)flavone and 4′-hydroxy-6-methoxyfurano(8,7-4″,5″)flavone, respectively, on the basis of the spectral evidence and they have been confirmed by synthesis.     

Changes in plasma membrane and microfilaments accompanying morphologic differentiation in Chinese hamster ovary (CHO) cells.

Studies on the application of the techniques of counter-current distribution (CCD) in aqueous two-phase systems and multiple sedimentation for the fractionation of metaphase chromosomes are presented. The two-phase systems were composed of aqueous solutions of Dextran 500 and poly(ethylene)glycol 6000 (PEG). It has been found that different groups of chromosomes differ in their distribution between the two phases and that the introduction of PEG with covalently attached positively or negatively charged groups provides a means of steering the distribution of chromosomes. A rough fractionation of chromosomes on the basis of size is possible by the technique of multiple sedimentation and this, in combination with CCD, yields 10 fractions of chromosomes. Partition and CCD in aqueous two-phase system separate chromosomes according to their surface properties and may prove useful for isolation of individual chromosomes in bulk.     

Fusion of two F-prime factors inEscherichia coli studied by electron microscope heteroduplex analysis

Summary A fused F prime factor was obtained from a mating of arecA donor carrying an F' factor containing the genesmetBJF, ppc andargECBH (KLF5) with arecA recipient carrying an F' factor containingatt80, trp andlac (F155). Lysogenization of this fused F-prime factor with cI⁸⁵⁷ h80 phage followed by thermoinduction produced the transducing phages 80dmetBJF and 80dppcargECBH. This kind of fusion provides a general procedure for the construction of transducing phages carrying genes from different regions of theE. coli genome. To understand the mechanism of this fusion, the parental F prime factors (F155 and KLF5) were analyzed by the electron microscope heteroduplex technique.F155 has a length of 176±3 kilobases including two substitutions. The F sequence 0 F-2.8 F has been substituted by 53 kb of chromosomal DNA including thelac operon and the F sequences 8.5 F-16.3 F has been substituted by 27 kb of a chromosomal sequence includingatt80 and thetrp operon.KLF5 contains 221±4 kilobases of DNA (molecular weight, 148 megadaltons). It contains complete F and the segment of theE. coli chromosome frompolA torif. The F sequence 2.8 F-8.5 F known to be involved in F specific recombination inrecA ⁺ andRecA backgrounds occurs twice on KLF5, once at each of the junctions of F DNA with chromosomal DNA. The population of closed circular plasmid molecules extracted from KLF5-containing strains is heterogeneous. It is proposed that this heterogeneity is due to intramolecular recombination events occurring in KLF5 between the duplicated 2.8 F-8.5 F sequences. Such recombination can account for the genetic instability of KLF5 observed in bothrecA ⁺ andrecA hosts. The F sequence 2.8 F-8.5 F (also called ) is one of the characterized integration sequences on F.A model for the fusion of the parental F prime factors is proposed in which recombination between sequences bringsatt80 close to themetBJF genes. This is followed by a deletion of an F'lac factor. The resulting fused F' factor still carries two sequences and is therefore expected to be unstable. The closed circular molecules isolated from the fused F' containing strains show two different sizes of molecules. Genetic and physical analyses of these molecules are in agreement with the predicted instability of the fused F' factor and the existance of the sequence in the 80dmet phages isolated from fused F' and previously analyzed by the electron microscope heteroduplex technique.