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21.
Mutations at the trkB and trkC loci of Escherichia coli produce an abnormal efflux of K+. The mutations are partially dominant in diploids and revert frequently by what appears to be intragenic suppression to the null state. The mutations can be reverted by insertion of Tn10 into the mutated gene, and spontaneous revertants are fully recessive to the mutant allele in diploids. K+ efflux produced by NEM* and by DNP* persists in strains with presumed null mutations at either locus, indicating neither gene product is the primary target for the effect of these inhibitors on K+ efflux. The results are consistent with the view that trkB and trkC encode independent systems for K+ efflux. Mutations at these loci alter regulation of the process so that K+ efflux occurs inappropriately. A second mutation to the null state abolishes this abnormal K+ efflux. These genes may encode K+/H+ antiporters, an activity postulated to mediate K+ efflux and demonstrated to exist in E. coli and other bacteria. 相似文献
22.
Edmond A. Goidl Christiane Samarut Ansbert Schneider-Gadicke Neal L. Hochwald G.Jeanette Thorbecke Gregory W. Siskind 《Cellular immunology》1984,85(1):25-33
Using hapten-reversible inhibition of plaque formation as an assay for auto-anti-idiotype antibody (anti-Id) and as a means for following idiotype (Id) expression, we have obtained evidence that following immunization with trinitrophenyl (TNP) conjugates (a) there are differences in Id expression in the anti-TNP antibody response to different TNP conjugates although there is some overlap; (b) different strains, although showing some differences in Id expression, tend to produce cross-reactive Ids, thus no obvious allotype linked inheritance of Id expression is observed in this heterogeneous immune response; (c) the auto-anti-Id produced following immunization with TNP-Brucella abortus or TNP-Ficoll tends to be of the IgG2a and IgG2b isotypes. 相似文献
23.
The 13C-n.m.r. spectra of asialo-GM1 and GM1-oligosaccharide are completely assigned and compared to those previously found for intact GM1 and for the series GM4, GM3, GM2, GM1, GD1a, GD1b, and GT1b. Removal of the ceramide residue from GM1 liberated a free, reducing aldehyde group, which was reflected in a doubling of the 13C-n.m.r. signals assignable to the d-glucose residue because of α,β equilibrium. The spectrum of asialo-GM1 lacks the resonances from the sialic acid residue, as expected; in addition, several resonances from the neutral gangliotetraglycosyl residue shifted to different field positions after removal of sialic acid from GM1. These resonances include that of C-4 of the inner β-d-galactosyl residue, and C-1 of the 2-acetamido-2-deoxy-d-galactosyl residue that is near the site of attachment of the sialosyl residue. The differences between the chemical shifts of the carbon resonances of oligomeric and monomeric saccharides, termed linkage shifts, provide a quantitative assignment aid. They are ~ of those for residues linked to sialic acid than those for residues linked to the neutral hexose chain. Correlations among linkage shifts for pairs of glycosidically-linked carbon atoms for asialo-GM1 and GM1-oligosaccharide were compared with those for the series of gangliosides GM4 to GT1b, and differences are noted for resonances for carbon atoms near the sialic acid residue. The spectrum of ganglioside GM1b, a positional isomer of GM1 whose 13C-n.m.r. spectrum has not yet been observed, is predicted. 相似文献
24.
The maturation of the ability of the B-cell population to re-express surface immunoglobulin (sIg) after its removal by treatment with rabbit anti-mouse immunoglobulin (RAMIg) was studied in LAF1, C57BL/6, and C57L mice. As demonstrated by previous workers, the B-cell population from immature mice failed to re-express sIg after treatment with RAMIg. We have shown that the age at which the B-cell population acquires the capacity to re-express sIg is different in different strains and that the order in which the B-cell population of the different strains acquires the capacity to re-express sIg is different from the order in which their B-cell populations acquire the capacity to produce high-affinity antibodies. This suggests that these represent distinct differentiation events in the development of the B-cell population. In all of the strains studied the maturation of the capacity to re-express sIg occurred in two steps. After the first maturation step the B-cell population was able to re-express sIg after treatment with RAMIg for 1 hr but did not re-express sIg after treatment with RAMIg for 24 hr. After the second maturation step the B-cell population could re-express sIg even after 24 hr treatment with RAMIg. It has been suggested by previous workers that the inability of the immature B-cell population to re-express sIg could represent one of the mechanisms responsible for the development of B-cell self-tolerance. It is suggested here that the existence of a period during which cells become tolerant only upon prolonged exposure to antigen could protect the developing B cells from becoming unresponsive to transiently experienced foreign antigens but still permit them to become tolerant to self antigens which are continuously present. 相似文献
25.
Loss and resynthesis of a developmentally regulated membrane protein (gp80) during dedifferentiation and redifferentiation in Dictyostelium 总被引:1,自引:0,他引:1
When developing cultures of Dictyostelium discoideum are disaggregated and resuspended in nutrient medium, they lose the capacity to rapidly reaggregate after 90 min, in a rapid and synchronous step referred to as the "erasure event." They then proceed to lose remaining developmentally acquired functions in a program of dedifferentiation culuminating with the loss of EDTA-resistant cohesion roughly 5 hr later. Immediately following the erasure event, cells can be stimulated to reenter the developmental program even though they still possess a number of developmentally acquired functions. These cells therefore appear to undergo dedifferentiation and redifferentiation simultaneously (D. R. Soll and L. H. Mitchell, 1982, Dev. Biol. 91, 183-190). In this report, we have employed an antiserum made against a developmentally acquired membrane glycoprotein, gp80, to examine whether gp80 is lost during dedifferentiation and whether it is either reutilized or resynthesized during redifferentiation. Results are presented which demonstrate that (1) when 9-hr developing cells are disaggregated and resuspended in nutrient medium, gp80 continues to accumulate for several hours after the erasure event, then is lost at roughly the same time as EDTA-resistant cohesion; (2) when cells are stimulated to reenter the developmental program immediately after the erasure event, both gp80 and EDTA-resistant cohesion are still lost according to the program of dedifferentiation, but are then reacquired soon afterwards according to the program of redifferentiation; (3) during redifferentiation, cells do not reutilize gp80 which had been synthesized during initial development; rather they synthesize gp80 de novo; and (4) developing cells of a dedifferentiation-defective variant, HI4, when disaggregated and resuspended in nutrient medium, retain gp80, EDTA-resistant cohesion, and the capacity to rapidly reinitiate aggregation for at least 12 hr. This last result indicates that the loss of gp80 is regulated by the dedifferentiation process and is not an independent response to disaggregation or the reintroduction of nutrients. Together, these results reinforce the conclusion that dedifferentiation and redifferentiation can function independently and simultaneously in the same cells. 相似文献
26.
本文描述了云南省条鳅亚科鱼类一新属和一新种。根据形态特征并结合区系间的相互关系,探讨了属的分类地位。 相似文献
27.
ARTHUR G. HUMES 《Zoological Journal of the Linnean Society》1996,118(1):59-82
Three new monotypic genera of copepods (Poecilostomatoida) are associated with the hermatypic shallow-water coral Psammocora (Stephanaria) logianensis near Noumea, New Caledonia: in the Anchimolgidae, Lipochaetes extrusus (antenna 4-segmented, endopods absent in legs 3 and 4) and Dumbeana undulatipes (antenna 3-segmcntcd, endopod of leg 3 with formula 0 1; 0–2; 1,11,2; leg 4 endopod with 0 1:1); and in the Rhynchomolgidae; Emunoa proknta (leg 4 endopod with 0 1;II, antenna 4-segmented, mandible witli outer pointed process and inner row of spines). Copepoda (primarily Poecilostomatoida and Siphonostomatoida, but also relatively few Cyclopoida and Harpacticoida) are very frequent associates or parasites of Scleractinia. At present 245 species from 48 scleractinian coral genera are known. Species of these copepod associates, their host genera, and localities, described since (and those not included in) previous publications of the author are listed. 相似文献
28.
29.
In many German forest soils low base saturation of CEC in deeper soil layers was reported and acidic deposition is seen as
the major cause of these findings. To test this hypothesis we sampled 5 New Zealand forest soils from pristine beech (Nothofagus fusca, N. menziesii, N. solandri) sites under climatic and geological conditions comparable to higher elevations in Germany. The soils developed from granite
and greywacke. Soil samples were analyzed for pH and the exchangeable cations were extracted with 1M NH4Cl. The base saturation of all soil profiles was very low, even in deeper layers and was thus similar to the patterns found
in many German forest soils. The pH was generally higher in the New Zealand soils as compared to Germany. The reason for the
depletion of base cations in deeper soil layers of New Zealand forest soils is most likely the leaching of base cations with
HCO3
- resulting from the dissociation of carbonic acid in connection with high amounts of seepage. Thus, under high rainfall conditions,
the low base saturation found in deeper layers of forest soils cannot exclusively be attributed to the effects of acidic depositions
and land use. ei]Section editor: R F Huettl 相似文献
30.