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Aflatoxins comprise a group of polyketide-derived carcinogenic mycotoxins produced byAspergillus parasiticus andAspergillus flavus. By transformation with a disruption construct, pXX, we disrupted the aflatoxin pathway inA. parasiticus SRRC 2043, resulting in the inability of this strain to produce aflatoxin intermediates as well as a major yellow pigment in the transformants. The disruption was attributed to a single-crossover, homologous integration event between pXX and the recipientA. parasiticus genome at a specific locus, designatedpksA. Sequence analysis suggest thatpksA is a homolog of theAspergillus nidulans wA gene, a polyketide synthase gene involved in conidial wall pigment biosynthesis. The conservedβ-ketoacyl synthase, acyltransferase and acyl carrier-protein domains were present in the deduced amino acid sequence of thepksA product. Noβ-ketoacyl reductase and enoyl reductase domains were found, suggesting thatpksA does not encode catalytic activities for processingβ-carbon similar to those required for long chain fatty acid synthesis. ThepksA gene is located in the aflatoxin pathway gene cluster and is linked to thenor-1 gene, an aflatoxin pathway gene required for converting norsolorinic acid to averantin. These two genes are divergently transcribed from a 1.5 kb intergenic region. We propose thatpksA is a polyketide synthase gene required for the early steps of aflatoxin biosynthesis.  相似文献   
13.
Endocytosis is the fundamental uptake process through which cells internalize extracellular materials and species. Neurodegenerative diseases (NDs) are characterized by a progressive accumulation of intrinsically disordered protein species, leading to neuronal death. Misfolding in many proteins leads to various NDs such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS) and other disorders. Despite the significance of disordered protein species in neurodegeneration, their spread between cells and the cellular uptake of extracellular species is not entirely understood. This review discusses the major internalization mechanisms of the different conformer species of these proteins and their endocytic mechanisms. We briefly introduce the broad types of endocytic mechanisms found in cells and then summarize what is known about the endocytosis of monomeric, oligomeric and aggregated conformations of tau, Aβ, α-Syn, Huntingtin, Prions, SOD1, TDP-43 and other proteins associated with neurodegeneration. We also highlight the key players involved in internalizing these disordered proteins and the several techniques and approaches to identify their endocytic mechanisms. Finally, we discuss the obstacles involved in studying the endocytosis of these protein species and the need to develop better techniques to elucidate the uptake mechanisms of a particular disordered protein species.  相似文献   
14.
To obtain general rules of peptide design using α,β-dehydro-residues, a sequence with two consecutive ΔPhe-residues, Boc-L -Val-ΔPhe–ΔPhe- L -Ala-OCH3, was synthesized by azlactone method in solution phase. The peptide was crystallized from its solution in an acetone/water mixture (70:30) in space group P61 with a=b=14.912(3) Å, c= 25.548(5) Å, V=4912.0(6) Å3. The structure was determined by direct methods and refined by a full matrix least-squares procedure to an R value of 0.079 for 2891 observed [I?3σ(I)] reflections. The backbone torsion angles ?1=?54(1)°, ψ1= 129(1)°, ω1=?177(1)°, ?2 =57(1)°, ψ2=15(1)°, ω2 =?170(1)°, ?3=80(1)°, ψ3 =7(2)°, ω3=?177(1)°, ?4 =?108(1)° and ψT4=?34 (1)° suggest that the peptide adopts a folded conformation with two overlapping β-turns of types II and III′. These turns are stabilized by two intramolecular hydrogen bonds between the CO of the Boc group and the NH of ΔPhe3 and the CO of Val1 and the NH of Ala4. The torsion angles of ΔPhe2 and ΔPhe3 side chains are similar and indicate that the two ΔPhe residues are essentially planar. The folded molecules form head-to- tail intermolecular hydrogen bonds giving rise to continuous helical columns which run parallel to the c-axis. This structure established the formation of two β-turns of types II and III′ respectively for sequences containing two consecutive ΔPhe residues at (i+2) and (i+3) positions with a branched β-carbon residue at one end of the tetrapeptide.  相似文献   
15.
Mycelium of Fusarium oxysporum grown on a glucose-containing medium lacked fructosyl transferase and invertase activities. Synthesis of fructosyl t  相似文献   
16.
Summary Two NAD-dependent alcohol dehydrogenases ADH-1 and ADH-2, under independent genetic control of genes designated as Adh-1 and Adh-2 located on chromosomes 4A, 4B and 4D, have been reported in aestivum wheat (Hart 1980). Only ADH-1 is expressed in developing seeds, dry seeds, pollen and germinating seedlings. ADH-2 can be induced in seedling roots or shoots under conditions of partial anaerobiosis or by certain chemicals. Expression of ADH-1 and ADH-2 isoenzymes was investigated in undifferentiated calli from aestivum and durum wheats, rye, triticale and also in in vitro regenerated roots and leaves from aestivum cultures. Wheat callus cultures originating from seed, mature and immature embryos, mesocotyl and root, as well as cultures grown on media containing different supplements did not show any variation in the overall expression of ADH-1 or ADH-2, although differences in the band intensities were observed. The callus isoenzyme pattern was similar to that observed in roots under anaerobic conditions. Both ADH-1 and ADH-2 were expressed in in vitro regenerated roots but were absent in regenerated leaves. Expression of ADH-1 and ADH-2 in wheat calli seems to be related to the type of differentiation.  相似文献   
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Centperazine or diethylcarbamazine, administered at various dose levels to rats inhibited the activity of succinate dehydrogenase significantly in 4 hrs in liver. Centperazine also inhibited the activity of cytochrome-c oxidase but stimulated the activity of benzo (a) pyrene hydroxylase in liver. In kidneys, activities of succinate dehydrogenase, cytochrome-c oxidase and aniline hydroxylase were significantly inhibited by centperazine only, however, the activity of benzo (a) pyrene hydroxylase was inhibited by both the drugs. These drugs had no effect on the activity of aminopyrene N-demethylase and cytochrome P-450 contents of liver and kidneys.  相似文献   
19.
Ni2+ inhibits electron-transport activity of isolated barley chloroplasts and this inhibition of electron transport by Ni2+ is distinctly different from other heavy metal ion (e.g., Pb2+, Cd2+, Zn2+)-induced inhibition of chloroplast function. Ni2+ inactivates Photosystem II (PS II) activity at a lower concentration than that required for the same extent of inhibition of Photosystem I (PS I)-mediated electron flow. Ni2+ induces changes in chlorophyll a (Chl a) emission characteristics and brings about a lowering of the Chl a fluorescence yield, and this lowering of Chl a fluorescence intensity is not relieved by the exogenously supplied electron donor NH2OH which donates electrons very close to the PS II reaction centres. Immobilization of the chloroplast membrane structure with glutaraldehyde fails to arrest the Ni2+-induced loss of PS II activity. Also, Ni2+-treated chloroplasts do not regain the ability to photoreduce 2,6-dichlorophenolindophenol even after washing of chloroplasts with buffer. These results indicate that unlike Zn2+ or Pb2+, Ni2+ induces alterations in the chloroplast photosynthetic apparatus resulting in an irreversible loss of electron-transport activity.  相似文献   
20.
The use in the literature of statistics and measures derived for the measurement and the analysis of inbreeding from data on gene frequency diversity and applied to data on surname diversity is discussed. To overcome the difficulties encountered with this approach, a simple mathematical model for analysing isonymy data is proposed. Finally some further measures of surname diversity are given based on measures developed for gene diversity analysis and for community diversity analysis in ecology.  相似文献   
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