摘要:

The isolation, characterization, and expression of a novel cDNA encoding aTrypanosoma cruzipolypeptide (TcAc2), homologous to various small stress proteins and glutathione S‐transferases, are described. The deduced amino‐acid sequence revealed two domains sharing 27% identity and an additional 27% similarity to each other suggesting that the molecule may have evolved from a single domain by a process of gene duplication and fusion. The TcAc2 cDNA was subcloned into the pGEX‐2T vector for expression inE coli.In vitrotranslation products of epimastigote mRNA, immunoprecipitated with anti‐TXepi serum, showed a major radioactive band of 52 kDa. Immunoprecipitation of [35S] methionine labelled epimastigote and trypomastigote antigens after pulse chase experiments, using anti‐TcAc2 fusion protein antibodies, showed that the protein is released into the culture medium. Moreover, Western blot analysis revealed a single band of 52 kDa with epimastigote, trypomastigote and amastigote antigens. Primary structure homology searches revealed that each TcAc2 domain contained within its N‐terminus significant homology toSolanum tuberosumpathogenesis‐related protein PRI, soybean heat shock protein 26‐A, auxin regulated clone pCNT103 fromNicotiana tabacumandDrosophila melanogasterglutathione S‐transferase 27 (GST27). This finding was supported by a comparison of hydrophobicity profiles of TcAc2 and these proteins. Most of them play a central role in protection mechanisms against stress. Based on the homology between TcAc2, glutathione S‐transferases (GST) and small stress proteins, it is likely that the TcAc2 gene product may play a crucial role in parasite's adaptation to its microenvironment. These molecules could be considered as members of the GST superfamily, where theT cruziprotein may take a particular place because of its intern

ISSN:0248-4900    

DOI:10.1016/0248-4900(94)90011-6

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

We have used CREST anti‐centromere sera, rabbit anti‐histone antibodies, and repetitive DNA analysis to study centromere structure in the flyMegaselia scalaris(Phoridae). In a panel of eight CREST sera, four were positive in immunofluorescence experiments for prekinetochores,iecentromeres in interphase nuclei. The access of the antibodies to CREST antigens may be compromised in the condensed state, since centromeres of prometaphase and metaphase chromosomes remained unstained. When Western blots of embryonic nuclei were probed with these four CREST sera, three of them showed a 17 kDa band. Human CENP‐A, likewise recognized by the CREST sera, is a 17 kDa protein. The remaining sera were negative for centromeres although some detected centrosomes and non‐histone chromosomal proteins not confined to the centromeres. The use of antibodies generated against histone H4 acetylated at four different sites of the N‐terminal domain revealed that heterochromatic regions ofM scalarismitotic chromosomes,iepericentric and NOR‐associated segments, are hyperacetylated. This is at variance with a variety of other systems, where transcriptionally active chromatin is hyperacetylated. Finally, a repetitive 165 base pair fragment was isolated from genomic DNA of the fly and sequenced. An oligonucleotide from this sequence mapped to the centromere region of interphase nuclei and the pericentric regions of condensed

ISSN:0248-4900    

DOI:10.1016/0248-4900(94)90012-4

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

A mutant strain ofDrosophila subobscurapossesses two mitochondrial genome types: a minority population (20%) identical to the wild strain mtDNA (15.9 kb), and a largely predominant population (80%) of shorter genomes (10.9 kb), presenting a deletion of more than 30% of its coding region. Study of tissular distribution of heteroplasmy shows it to be identical — about 80% — in the head (nervous tissue) and thorax (muscles). On the other hand, a lower percentage (64%) is observed in the ovaries. The strain is apparently unaffected despite this massive loss of genes, coding for four tRNA and for complex I and III subunits. Contrary to observations of similar situations in man, the mutant strain shows no accumulation or structurally abnormal mitochondria. Furthermore, cytochemical studies fail to detect mitochondria devoid of cytochrome oxidase activity (COX−). Finally, mitoribosome populations are identical in mitochondria from both strains. These results suggest that, in the mutant strain, there are no mitochondria containing deleted genomes only: heteroplasmy would thus be intramitochon

ISSN:0248-4900    

DOI:10.1016/0248-4900(94)90013-2

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The urinary bladder of the aquatic toadXenopus laevisis known to exhibit a low permeability to water and a poor sensitivity to antidiuretic hormone. In order to precise the characteristics and the specific cellular mechanisms of this reduced hydroosmotic response we used a sensitive volumetric technique to monitor net water flow and studied the correlation between the anti‐diuretic hormone (ADH)‐induced net water flow and the fine ultrastructural appearence of the urinary bladder epithelium. Transmural net water flow was entirely dependent on the osmotic gradient across the preparation and not on the hydrostatic pressure difference. We observed the existence of a low but significant hydro‐osmotic response to arginine vasopressin. Freeze‐fracture electron microscopy demonstrated the presence of typical aggrephores in the subapical cytoplasm. The response to the hormone was accompanied by the appearance of typical intramembrane aggregates into the apical plasma membrane. Water permeability increase and apical aggregate insertion were both slowly but fully reversible. Except for the multilayered structure of the epithelium and the particularly low response to antidiuretic hormone, all the studied permeability and ultrastructural characteristics of the bladder were thus very similar to those observed in other sensitive epithelia such as the amphibian bladder and skin and the mammalian collecting duct which exhibit a high hydro‐osmotic response to th

ISSN:0248-4900    

DOI:10.1016/0248-4900(94)90014-0

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Following the previous ultrastructural demonstration of the presence of arylsulphatase (Asase) activities in Kurloff cells (KC) and of their quasi‐exclusive localization in the Kurloff body (KB), this work investigates their biochemical and zymographic properties after extraction from purified KC suspensions. Using the discriminative inhibitory conditions of both the Baum or LeeVaupel and Conzelmann methods, nitrocatechol sulphate hydrolyzing enzymes of the KC were assumed to belong to the B class of the type II Asase alone. After electrophoretic separation under non‐denaturing conditions in a 4–23% polyacrylamide gel, they were characterized by 55 kDa and 62 kDa zymographic bands. After isoelectric focusing, ‘classical’ cationic isoforms (pI8.5) and two anionic isoforms (pI4.4 and 4.6) were observed on zymograms. As expected for class B Asase, the different zymographic forms of KC Asase were only recovered in the unadsorbed fraction after anion‐exchange chromatography on DEAE‐cellulose column equilibrated with high ionic strength buffer. Their Km(2.1 mM), their optimum pH (5.8) and their inhibitions by sulfite, phosphate, sulphate and ascorbic acid as well as their slight stimulation by AgNO3were also characteristic of this class of Asase. Finally, chondroitin4‐sulphate was shown to potentially be a physiological substrate for these ly

ISSN:0248-4900    

DOI:10.1016/0248-4900(94)90015-9

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Gold particles were prepared, dried on grids and shadowed at 45° with a 1.2 nm platinum‐carbon (Pt‐C) film using the shadowing conditions previously described for the freeze‐fracture of gastric parietal cell membranes. The particle diameters and the particle shadow widths and lengths were measured using an image analysis system. Statistical analysis of 2000 diameters, shadow widths and shadow lengths indicated that a homogenous population of particles had a normal frequency distribution of diameters (mean diameter 14.5 ± 1.5 nm) and that the Pt‐C shadowing transformed that normal curve into a log‐normal frequency distribution of shadow widths. The frequency distribution of shadow lengths was log‐normal too. We conclude that a statistical partition of experimental frequency distributions of particle shadow widths and lengths of natural membranes to determine the number and parameters of individual components should involve log‐normal subdistributions rather t

ISSN:0248-4900    

DOI:10.1016/0248-4900(94)90016-7

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

In a previous work, resting and acid‐secreting rabbit gastric mucosa were freeze‐fractured and shadowed at 45° with Pt‐C. The shadow widths of proteic particles of tubulovesicle and canaliculus membranes were measured and compared. It was concluded that the frequency distributions of widths are significantly different in resting and secreting membranes and that each distribution accounts for several subpopulations of homogenous particles. In the present study, an attempt is made to describe the experimental distributions as a mixture of those of two major proteins, say A and B and their aggregates (AA, AB and BB). The modelling, although simple, gave a very satisfactory statistical fit between observed and computed distributions. The comparison of parameters calculated from histamine and ranitidine experimental data further improves the fits and finally, component A accounts for 69% of the particles. Most replica of A particles are heart‐shaped and the median shadow widths are 6.1 and 6.8 nm in canaliculus and tubulovesicles respectively. The component B accounts for 31% of the particles. They mainly appear as small barrels and the median shadow widths are 8.8 and 10.3 nm in canaliculus and tubulovesicles respectively. According to calculated parameters and observed particle replica, the onset of secretion does not change the relative ratio of proteins but changes their shapes. Component A should be the (H+, K+)ATPase whereas debate on the identity of B is w

ISSN:0248-4900    

DOI:10.1016/0248-4900(94)90017-5

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Atomic force microscopy (AFM) has been used to image the surface of thin sections of fungal infected plant tissue, with or without post‐embedding immunocytochemical labeling with gold conjugates. Plant and fungal cells are easily identified from their size, shape and roughness. The cellular shape is similar to that observed by light or electron microscopy (LM or EM) and some internal organelles can even be individualized. The gold beads are easily observed and counted. Their dimensions varied according to the roughness of the surface, but fit with the expected size

ISSN:0248-4900    

DOI:10.1016/0248-4900(94)90018-3

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Observations of intact reconstituted and native collagen fibres were performed with the atomic force microscope. The results are compared between the two types of fibres and with those obtained previously with the electron microscope on freeze‐etched or negative stained samples. Some of the findings presented here indicate that the specimens observed in air with the atomic force microscope were still in a hydrated stat

ISSN:0248-4900    

DOI:10.1016/0248-4900(94)90019-1

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The ultrastructure and mechanosensitivity of a sensory organ in a terrestrial isopod are investigated. The mechanosensitivity of this sensory organ is demonstrated. Seven sensory cells are observed; one of them displays unusual ultrastructural features, a lamellar ciliary root and a tubular body‐like structure. The six other sensory cells are similar to usual chemosensitive cells. No sensory cell presents the characteristic cytological features of crustacean mechanosensitive exteroceptor

ISSN:0248-4900    

DOI:10.1016/0248-4900(94)90020-5

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY