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[en] Purine nucleoside phosphorylases (PNPs) catalyze the reversible phosphorolysis of nucleosides and are key enzymes involved in nucleotide metabolism. They are essential for normal cell function and can catalyze the transglycosylation. Crystals of E. coli PNP were grown in microgravity by the capillary counterdiffusion method through a gel layer. The three-dimensional structure of the enzyme was determined by the molecular-replacement method at 0.99 Å resolution. The structural features are considered, and the structure of E. coli PNP is compared with the structures of the free enzyme and its complexes with purine base derivatives established earlier. A comparison of the environment of the purine base in the complex of PNP with formycin A and of the pyrimidine base in the complex of uridine phosphorylase with thymidine revealed the main structural features of the base-binding sites. Coordinates of the atomic model determined with high accuracy were deposited in the Protein Data Bank (PDB-ID: 4RJ2).
[en] A facile method for the introduction of deuterium at the Csub(4') position of uridine and its derivatives involves the reaction of appropriately protected 4',5'-unsaturated pyrimidine nucleosides with B2D6, followed by hydrogen peroxide oxidation under alkaline conditions. The method described herein is also adaptable to the introduction of tritium at Csub(4') position of pyrimidine nucleosides for use in mechanistic studies of DNA-degrading drugs. (author)
[en] 7'-Aldehyde-nucleosides analogue (2a, 2c) were synthesized from 6-N-benzoyl-2'-3'-O-iso-propylideneadenosine and uridine. The condensation of 2 with ethoxycarbonylmethylene Wittig reagent produced the adenosine and uridine analogues containing extended conjugated diene and ethoxycarbonyl group, ethyl-1',5',6',7',8'-pentadeoxy-1'-(adenin-9-yl)-β-D-ribo-nona-5'(E),7'(E) - dienofuranuronate (4b) and ethyl-1',5',6',7',8'-pentadeoxy-1'-(uracil-1-yl)-β-D-ribo-nona-5'(E),7'-(E) - dienofuranuronate (4c). 9-(8',8'-dibromo-5',6',7',8'-tetradeoxy-β-D-ribo-octa-5'(E),7'(E)-diene) nucleosides (6b, 6c) were also prepared from 2 with similar method.
[en] The results about the RNA biosynthesis of pimiento ring virus are analysed. The possible virus influence on the nucleolus, mitochondria and chloroplast of the cellular RNA is studied by electron microscopy radio-authogram. The presence of the virus in the cell seems to modify 3H-uridine transport to hostess cell interior. (M.A.C.)
[pt]Analisam-se os resultados sobre a biossintese do RNA do virus do anel do pimentao (VAP) e a possivel influencia do virus sobre o RNA celular no nucleolo, mito-condrio e cloroplasto atraves de radioautogramas obtidos ao microscopio eletronico. Conclui-se que a presenca do VAp na celula parece alterar o transporte de uridina - 3H para o interior da celula hospedeira. (M.A.C.)
[en] Highlights: • Crystal structure of MORF2 is determined at 2.4 Å. • MORF2 forms dimer through hydrophobic interaction. • Dimerization interface of MORF2 overlaps with its PPR interacting site. • A dimer-to-monomer transition is implicated for MORF2's role in RNA editing. RNA editing is a post-transcription process that alters the genetic information on RNA molecules. In plastids and mitochondria of flowering plants, the multiple organellar RNA editing factors (MORFs) interact with the PLS-type pentatricopeptide repeat (PPR) proteins and participate in RNA editing of cytidine-to-uridine conversion. The PPR proteins recognize cytidine targets around the editing sites, and the MORF proteins modulate the RNA-binding activity of the PPR proteins. Here, we report the structure of the Arabidopsis thaliana chloroplast MORF2 at 2.4 Å resolution. The structure, adopting typical MORF-box fold as observed in mitochondrial MORF1 and chloroplast MORF9, reveals an MORF1-like dimerization mode. The difference between the two dimerization modes can be attributed to F157 (corresponding F162 in MORF1 and W160 in MORF9), which causes a 60° shift upon dimerization. This observation, together with the PPR–MORF2 model, suggests a dimer-to-monomer transition during RNA editosome formation.
[en] A rapid method of autoradiography for squash preparations of Drosophila larval polytene chromosomes has been described. The method utilizes treatment of the preparation with scintillation cocktail, Omnifluor-toluene mixtures, prior to developing the autoradiograms. The autoradiograms can be obtained with near maximum efficiency within 72 hr. The suggested optimum time of exposure and pre-treatment is 24 hr. dry exposure plus 48 hr. in the fluid. The percentage of 3H-uridine labelled cells by this method appears to be about 86 to 92% as compared to about 95% by conventional method of 14 to 16 days dry exposure. The resolution seems to be better, and location of grains appears to be undisturbed. (author)
[en] Some aspects of the pathological process of the infectious flacherie virus in the midgut epithelial cells of the silkworm (Bombyx mori L., 1758 (Lep., Bombycidae)) as well as the site of the viral RNA synthesis were investigated. Electron microscope observation of these inclusion bodies showed that they were surrounded by a single membrane and containing many vesicles and virus particles. The nucleus of the cells infected with the virus exhibited higher electron dense masses than the healthy ones. The site of the viral RNA synthesis. Actinomycin D, at the used concentration, selectively blocked the cell RNA synthesis without affecting the virus RNA synthesis. The inhibition found was about 60%. The data obtained indicated that the viral RNA synthesis occurs in the nucleus of the midgut epithelial cells of the silkworm larvae. (author)
[en] The appearance of perinucleolar electron-dense spots in the nuclei of macroconidia of Neurospora crassa incubated at 460C and their disaggregation after shift-down to 250C have been investigated by high-resolution autoradiography after (5-3H) uridine pulses with or without chase periods. The RNA of these ribonucleoprotein-rich dense spots has been found to originate mainly from the heat-sensitive nucleolus; after return to 250C, the nucleolar activity was recovered and the RNA material stored either in an unprocessed or a mature rRNA form in the dense spots was found to be progressively extruded into the cytoplasm. (Author)