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11.
INTERSPECIFIC TRANSFORMATION IN BACILLUS 总被引:5,自引:0,他引:5
Marmur, J. (Brandeis University, Waltham, Mass.), E. Seaman, and J. Levine. Interspecific transformation in Bacillus. J. Bacteriol. 85:461-467. 1963.-Deoxyribonucleic acids (DNA) from various species of the taxonomic group Bacillaceae were examined for base composition, ability to carry out interspecific transformation, and formation of molecular hybrids in vitro. The minimal requirement for genetic compatibility among different species and for DNA interaction (both reflecting base sequence homologies) is the similarity of the guanine plus cytosine contents of the DNA. The close correlation between the ability of DNA to be competent in interspecific transformation and to form hybrid molecules on denaturation and annealing provided a rational approach to the study of genetic relationship among organisms for which no genetic exchange has yet been demonstrated. Any or all of the criteria (base composition of DNA, transformation, molecular hybrid formation) can be used as tools in the taxonomic assessment of closely related microorganisms. 相似文献
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Natural killing by mouse spleen cells can be stimulated in vivo by interferon or by agents that stimulate interferon, such as poly I.C. Natural killing can be suppressed in vivo by the sustained administration of 17 beta-estradiol. In BALB/c mice that had been treated with 17 beta-estradiol for 10 weeks, natural killing did not respond to intravenous poly I.C, although stimulation of circulating interferon was equal to controls. Estradiol, then, does not block interferon production but does suppress the response of natural killer cells to interferon. It is suggested that estrogens either block the maturation of natural killer cells or reduce the number of natural killer cell precursors. 相似文献
14.
NKR-P1, an activating molecule on rat natural killer cells, stimulates phosphoinositide turnover and a rise in intracellular calcium 总被引:13,自引:0,他引:13
J C Ryan E C Niemi R D Goldfien J C Hiserodt W E Seaman 《Journal of immunology (Baltimore, Md. : 1950)》1991,147(9):3244-3250
NKR-P1 is a 60-kDa homodimer expressed on all rat NK cells. Previous studies by others suggest that NKR-P1 may play a role in NK cell activation because antibody to NKR-P1 stimulates the release of granules from NK cells, and anti-NKR-P1 causes redirected lysis by activated NK cells against targets that express FcR. To examine the mechanism of transmembrane signaling by NKR-P1, we studied the rat NK cell line, RNK-16. We here demonstrate that F(ab')2 antibody to NKR-P1 stimulates phosphoinositide turnover and a rise in intracellular calcium within RNK-16 cells. The response is augmented by cross-linking the F(ab')2 antibody. The phosphoinositide/calcium pathway is also stimulated by NKR-P1 in activated rat NK cells, although no response is detectable in polymorphonuclear cells, which also express NKR-P1. We also demonstrate that RNK-16 cells kill the anti-NKR-P1 (3.2.3) hybridoma and that exposure to the hybridoma target cells stimulates phosphoinositide turnover in RNK-16 cells. Both killing and phosphoinositide turnover are inhibited by F(ab')2 anti-NKR-P1, implicating NKR-P1 in both responses. In contrast, neither cytotoxicity nor phosphoinositide turnover is appreciably blocked by F(ab')2 anti-NKR-P1 in response to YAC-1 targets. Thus, with either target, killing is linked to phosphoinositide turnover, but killing of YAC-1 involves pathways that differ from those that direct killing of the anti-NKR-P1 hybridoma. Our studies support the hypothesis that NKR-P1 may serve as an activating cell-surface receptor on NK cells, and they clarify the mechanisms by which it activates NK cells. 相似文献
15.
Inland salt waters of southern Africa 总被引:5,自引:5,他引:0
Inland salt lakes are widely distributed in southern Africa: they are particularly common in South Africa, but many occur
in Namibia and Botswana. All are shallow, and most are ephemeral with salinities that are not very high (mostly < 50 g l−1). Fringing zones of halophytes or submerged macrophytes are neither well-developed nor taxonomically diverse. The Cyanobacteria,
especially Nodularia spumigena, often dominate the phytoplankton. The fauna of the Makgadikgadi area (northeast Botswana) is diverse and is similar to that
of East African salt lakes. The aquatic fauna of salt water south of the Makgadikgadi Basin, on the other hand, is extremely
depauperate, has no well-defined assemblage confined to saline waters, and appears mostly to comprise tolerant freshwater
forms. Lovenula falcifera and Metadiaptomus transvaalensis (diaptomid copepods), Moina micrura (Cladocera) and Brachionus plicatilis (Rotifera) are frequently encountered zooplankton species, a few species of insects (Anisops sp., beetles, chironomids and ephydrids) are the principal non-planktonic macroinvertebrates. Artemia ‘salina’ is occasionally present, but may be an introduced form. The avifauna, in contrast to the aquatic macroinvertebrate fauna,
is rich, with the greater and lesser flamingo often common. 相似文献
16.
Janis E. Lochner Geoffrey V. F. Seaman Philip Blume Arthur Malley 《Cell biochemistry and biophysics》1982,4(1):15-24
Concanavalin A, at extremely low concentrations, will produce significant increases in the electrophoretic mobility of murine
splenic T lymphocytes. It has been established that the alteration in cellular surface charge is mediated by a factor produced
by those lymphocytes that have reacted directly with con A. We originally conjectured that the mobility change might be the
consequence of an alteration in the distribution of the charged moieties of membrane glycoproteins. The results of experiments
conducted at low temperature raise some questions about this mechanism. Further experiments have been performed to establish
the nature of the physicochemical alterations in the peripheral zone of the factor-stimulated lymphocytes that are manifest
as changes in cellular surface charge. The results of these studies indicate that, subsequent to the interaction of T lymphocytes
with con A, there is a reduction in the number of positively charged amino groups effective at the electrophoretic surface
of the cells. 相似文献
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Dan H. Barouch Kathryn E. Stephenson Erica N. Borducchi Kaitlin Smith Kelly Stanley Anna G. McNally Jinyan Liu Peter Abbink Lori F. Maxfield Michael S. Seaman Anne-Sophie Dugast Galit Alter Melissa Ferguson Wenjun Li Patricia L. Earl Bernard Moss Elena E. Giorgi James J. Szinger Leigh Anne Eller Erik A. Billings Mangala Rao Sodsai Tovanabutra Eric Sanders-Buell Mo Weijtens Maria G. Pau Hanneke Schuitemaker Merlin L. Robb Jerome H. Kim Bette T. Korber Nelson L. Michael 《Cell》2013
20.