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171.
172.
John M. Fairbrother Réal Lallier Linda Leblanc Mario Jacques Serge Larivière 《FEMS microbiology letters》1988,56(3):247-252
Abstract The production of fimbrial antigen F165 by Escherichia coli strains was found to be dependent on the composition of the culture medium and was repressed in the presence of alanine or high levels of glucose, in anaerobic conditions or at growth temperatures of lower than 37°C. Optimal F165 production was found on a minimal medium containing 1% (w/v) casamino acids (MD-1). F165 antigen was isolated from bacteria by mechanical shearing, precipitated with ammonium sulfate, and purified by deoxycholate treatment and gel filtration on Superose 12. The purified fimbriae retained their native morphology as observed by electron microscopy and consisted of two separate protein subunits with apparent molecular weights of 17 500 and 19 000 on sodium dodecyl sulfate-polyacrylamide gels. 相似文献
173.
Molecular organisation of the quinic acid utilization (QUT) gene cluster in Aspergillus nidulans 总被引:9,自引:0,他引:9
Alastair R. Hawkins Heather K. Lamb Melanie Smith John W. Keyte Clive F. Roberts 《Molecular & general genetics : MGG》1988,214(2):224-231
Summary The functional integrity of the QUTB gene (encoding quinate dehydrogenase) has been confirmed by transformation of a qutB mutant strain. The DNA sequence of the contiguous genes QUTD (quinate permease), QUTB and QUTG (function unknown) has been determined and analysed, together with that of QUTE (catabolic 3-dehydroquinase). The QUTB sequence shows significant homology with the shikimate dehydrogenase function of the complex AROM locus of Aspergillus nidulans, and with the QA-3 quinate dehydrogenase and QA-1S (repressor) genes of Neurospora crassa. The QUTD gene shows strong homology with the N. crassa QA-Y gene and QUTG with the QA-X gene. QUTD, QUTB, and QUTG, QUTE form two pairs of divergently transcribed genes, and conserved sequence motifs identified in the two common 5 non-coding regions show significant homology with UAS
GAL
and UAS
QA
sequences of the Saccharomyces cerevisiae and N. crassa Gal and QA systems. In addition, conserved 5 sequences homologous to the mammalian CAAT box are noted and a previously unreported conserved 22 nucleotide motif is presented. 相似文献
174.
Marion J. Couch Bendicht U. Pauli Ronald S. Weinstein John S. Coon 《Journal of cellular biochemistry》1988,37(2):213-223
Murine squamous carcinoma cells (KLN205) grown in a medium supplemented with the retinoid, 13-cis retinoic acid (RA), had dose-dependent, selective increases in the expression of certain lectin receptors, which correlated with a dramatic decrease in the ability to form pulmonary colonies (P ?.0003) (Couch MJ, Pauli BU, Weinstein RS, Coon JS: JNCI, 78:971 ?977, 1987). These findings suggest a possible relationship between the RA-induced glycoconjugate alterations and the decreased experimental metastatic behavior. We further define the mechanism of RA's action. The finding that RA treatment (5 × 10?6 M, 5 × 10?7 M) did not perturb the cell cycle of KLN205 cells provides further proof that the decreased metastatic behavior is not attributable to any inhibition in the rate of growth or to alterations in the cell cycle. Furthermore, since stable subpopulations with variable lectin binding could not be detected, the mechanism of RA's action does not appear to be due to selection of variant tumor-cell subpopulations. Finally, in a scries of experiments designed to determine the reversibility of the RA treatment, the RA-induced decrease in metastatic behavior reverted back to a more metastatic state in the same time frame (3 days) as the reversion of the RA-induced changes in cell-surface glycoconjugate expression. This reversion provides further evidence for a close relationship between the RA-induced modulation of tumor cell-surface glycoconjugate expression and the decreased metastatic behavior; it suggests that transient, reversible modulation of the tumor cell surface may play a role in determining metastatic behavior. 相似文献
175.
176.
John Marks 《BMJ (Clinical research ed.)》1988,296(6615):132-133
177.
178.
179.
John Greenman Nancy Hogg Suzanne Nikoletti Christopher Slade George Stevenson Martin Glennie 《Cancer immunology, immunotherapy : CII》1992,34(6):361-369
Summary The three forms of Fc receptor carried by monocytes (FcRI, II) and natural killer (NK) cells (FcRIII) are all capable of mediating cell lysis. Here we compare the use of F(ab)2 bispecific antibodies, specifically targetting individual FcR, and chimeric IgG mouse/human antibodies which are capable of targetting all FcR, for their ability to mediate target cell destruction. The derivatives are prepared by linking hinge sulphydryl residues via tandem thioether bonds, using a bismaleimide crosslinker: Fab from an anti-FcR mAb linked to Fab from a common anti-target mAb (BsAb), or Fab from the common anti-target mouse antibody linked to human Fc (FabFc or bisFabFc). All the derivatives targetting chick red blood cells gave efficient lysis, although different effector cell donors yielded differences in both the lytic levels achieved and the comparative efficiencies of derivatives. In contrast, significant lysis of the guinea pig lymphoblastic leukaemia, L2C, regularly resulted only via the anti-FcRIII BsAb and the chimeric derivatives. These results suggest that the chimeric, Fc-containing derivatives mediate tumour cell lysis principally through FcRIII on NK cells. This is in contrast to the situation with the chick red blood cells where the chimeric derivatives appear capable of lysing erythrocytes by utilizing either monocytes or NK cells, because significant (50%) lysis occurred with effector cell populations magnetically depleted through either FcRII or FcRIII. A major difference between these two types of antibody derivative was their ability to function in the presence of high concentrations of normal human Fc. The lysis mediated by BsAb reactive with FcRI or II was unaffected by the presence of human Fc at 2.5 mg/ml (a concentration comparable with that yielded by IgG in plasma) whereas the BsAb recognizing FcRIII and all the Fc-containing derivatives were completely inhibited.This work has been supported by Tenovus, the Cancer Research Campaign, the Leukaemia Research Fund, Italfarmaco, Milano, Italy and the Imperial Cancer Research Fund 相似文献
180.
Calling song and selective phonotaxis in the field crickets,Gryllus firmus andG. pennsylvanicus (Orthoptera: Gryllidae) 总被引:1,自引:1,他引:0
The field cricket species, Gryllus firmusand G. pennsylvanicus,occur in a mosaic hybrid zone that roughly parallels the eastern slope of the Appalachian mountains in the northeastern United States. It is important to know what role, if any, the calling song plays in mate choice in sympatric and allopatric populations. In this report, we present results on the variability of calling song properties along transects across this hybrid zone. We also present the results of experiments on phonotactic selectivity of females from an allopatric population of G. firmus.The male calling song of allopatric G. firmuswas significantly slower in temporal rhythm (i. e., chirp and pulse repetition rates) and lower in pitch (i.e., dominant frequency) than that of allopatric G. pennsylvanicus.Calling song properties of males recorded in the hybrid zone varied considerably in temporal and spectral properties. In two-stimulus (choice) phonotaxis experiments, allopatric females of G. firmuspreferred synthetic calling songs with conspecific pulse repetition rates over songs that had lower and higher pulse rates. This preference persisted even when the sound pressure levels of alternative stimuli were unequal. Therefore, allopatric females of G. firmuscan discriminate between conspecific and heterospecific calling songs. Whether or not this same selectivity is present in sympatric populations remains unclear. Investigations of phonotactic selectivity in other allopatric and sympatric populations of both species are currently under way. 相似文献