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981.
David A. Watson Vivek Kapur Daniel M. Musher James W. Jacobson James M. Musser 《Current microbiology》1995,31(4):251-259
This paper reports the cloning and sequencing of a region of DNA from Streptococcus pneumoniae serotype 3 surrounding transposon Tn916, insertion of which was previously shown to result in lack of expression of the extracellular capsule. Sequence analysis revealed that the transposon inserted into a consensus insertion site 71 bp from the 5 end of the cloned fragment. Within the clone, 3 downstream regions from two different pneumococcal lytA genes were identified, as well as a putative 194 AA open reading frame (ORF1). Moreover, two copies of the repeat element BOX, oriented in opposite directions, were located immediately 3 of orf1. Within the region bounded by the first pair of internal sequencing primers, analysis revealed that the fragment amplified by PCR was always of the same size. Moreover, Southern blotting showed that for all serotypes examined to date, homology exists with the cloned fragment. These results indicate that this region of the chromosome is highly conserved and, taken together with other independently derived data, suggest that interruptions or deletions within this DNA lead to unencapsulation. 相似文献
982.
Charles E. Sasser James G. Gosselink Erick M. Swenson D. Elaine Evers 《Wetlands Ecology and Management》1995,3(3):171-187
Floating marshes occur over 70% of the western Terrebonne Basin, Louisiana, USA, freshwater coastal wetlands. They are of several types: A free-floating thick-mat (45–60 cm) marsh dominated by Panicum hemitomon and Sagittaria lancifolia; a thick mat marsh dominated by Panicum hemitomon and Sagittaria lancifolia that floats part of the year, but whose vertical floating range is damped compared to adjacent water; and an irregularly-floating thin mat (< 30 cm) dominated by Eleocharis spp. in the spring and Ludwigia leptocarpa and Bidens laevis in the summer and fall. Floating mats must be almost entirely organic in order to be buoyant enough to float. The western Terrebonne wetlands receive large winter/spring supplies of suspended sediments from the Atchafalaya River. Even though sediment concentrations in the adjacent bayou are as high as 100 mg l–1, the Panicum hemitomon/Sagittaria lancifolia free-floating marsh probably receives no over-surface sediments since it floats continuously. The bulk density data of the damped-floating marsh, however, suggest some mineral sediment input, probably during winter when this marsh is submerged. These two types of floating marsh could not have developed in the present sediment regime of the Atchafalaya River, but as long as they remain floating can continue to exist. Thin floating mats are found in areas receiving the least sediment (<20 mg 1–1 suspended sediment concentration in adjacent bayous). This low sediment environment probably made possible their formation within the past 20 years. They may represent a transitional stage in mat succession from (1) existing thick-mat floating marsh to a degrading floating marsh, or (2) a floating marsh developing in shallow open water.Corresponding editor: D. Whigham 相似文献
983.
We studied the winter resource selection of muskoxen Ovibos moschatus in the High Arctic using a nested hierarchy of spatial scales 1) population range, 2) travel routes, 3) feeding sites (l e clusters of feeding craters), 4) feeding craters, and 5) diet (I e plant species) We found that, generally, patterns of selection remained consistent across all levels At successively smaller scales, muskoxen selected for higher graminoid abundance and particularly for thinner, softer snow cover, although we did not reject the hypothesis of random travel route selection Muskoxen uncovered forages from beneath the snow cover, by cratering, near the flonstic and nival extremes of availability Selection was consistently biased toward use of water sedge, Carex aquatilis As scale changed, however, muskoxen showed reversals of preference for some other forage species Diet was dominated by C aquatilis and cotton sedge, Eriophorum angustifolium , species characteristic of lowland meadows During spring melt, muskoxen moved to snow-free uplands to feed Dietary quality, as revealed by fecal nitrogen, increased at this time The consistency of the results across scales implied that these local levels of habitat selection occurred within one scaling domain 相似文献
984.
Mauseth James D. Uozumi Yoriko Plemons Brandon J. Landrum James V. 《Journal of plant research》1995,108(4):517-526
Wide-band tracheids are a specialized tracheid type in which an annular or helical secondary wall projects deeply into the
cell lumen. They are short, wide and spindle-shaped, and their bandlike secondary walls cover little of the primary wall,
leaving most of it available for water diffusion. Wide-band tracheids appear to store and conduct water while preventing the
spread of embolisms. They may be the most abundant tracheary element in the xylem, but they are always accompanied by at least
a few vessels. Typically, fibers are absent wherever wide-band tracheids are present. Wide-band tracheids occur in the primary
and secondary xylem of succulent stems, leaves and roots in genera of all three subfamilies of Cactaceae but were not found
in the relictual genusPereskia, which lacks succulent tissues. In the large subfamily Cactoideae, wide-band tracheids occur only in derived members, and
wide-band tracheids of North American Cactoideae are narrower and are aligned in a more orderly radial pattern than those
of South American Cactoideae. Wide-band tracheids probably arose at least three times in Cactaceae. 相似文献
985.
He Liu H. Peter Spielmann Nikolai B. Ulyanov David E. Wemmer Thomas L. James 《Journal of biomolecular NMR》1995,6(4):390-402
Summary The effect of experimental and integration errors on the calculations in interproton distances from NOE intensities is examined. It is shown that NOE intensity errors can have a large impact on the distances determined. When multiple spin (spin diffusion) effects are significant, the calculated distances are often underestimated, even when using a complete relaxation matrix analysis. In this case, the bias of distances to smaller values is due to the random errors in the NOE intensities. We show here that accurate upper and lower bounds of the distances can be obtained if the intensity errors are properly accounted for in the complete relaxation matrix calculations, specifically the MARDIGRAS algorithm. The basic MARDIGRAS algorithm has been previously described [Borgias, B.A. and James, T.L. (1990) J. Magn. Reson., 87, 475–487]. It has been shown to provide reasonably good interproton distance bounds, but experimental errors can compromise the quality of the resulting restraints, especially for weak cross peaks. In a new approach introduced here, termed RANDMARDI (random error MARDIGRAS), errors due to random noise and integration errors are mimicked by the addition of random numbers from within a specified range to each input intensity. Interproton distances are then calculated for the modified intensity set using MARDIGRAS. The distribution of distances that define the upper and lower distance bounds is obtained by using N randomly modified intensity sets. RANDMARDI has been used in the solution structure determination of the interstrand cross-link (XL) formed between 4-hydroxymethyl-4,5,8-trimethylpsoralen (HMT) and the DNA oligomer d(5-GCGTACGC-3)2 [Spielmann, H.P. et al. (1995) Biochemistry, 34, 12937–12953]. RANDMARDI generates accurate distance bounds from the experimental NOESY cross-peak intensities for the fixed (known) interproton distances in XL. This provides an independent internal check for the ability of RANDMARDI to accurately fit the experimental data. The XL structure determined using RANDMARDI-generated restrains is in good agreement with other biophysical data that indicate that there is no bend introduced into the DNA by the cross-link. In contrast, isolated spin-pair approximation calculations give distance restraints that, when applied in a restrained molecular dynamics protocol, produce a bent structure.Abbreviations NOE
nuclear Overhauser effect
- SD
standard deviation
- HMT
4-hydroxymethyl-4,5,8-trimethylpsoralen
- XL
psoralen-DNA interstrand cross-link 相似文献
986.
987.
988.
Peptides inhibit selectin-mediated cell adhesion in vitro, and neutrophil influx into inflammatory sites in vivo 总被引:1,自引:0,他引:1
Briggs John B.; Oda Yuko; Gilbert James H.; Schaefer Mary E.; Macher Bruce A. 《Glycobiology》1995,5(6):583-588
The selectins are cell adhesion molecules whose carbohydrate-bindingdomain (C-type lectin) is thought to be involved in leukocyteadhesion to activated vascular endothelium in the inflammatoryprocess. A series of peptides, based on a conserved region (48YYWIGIRK55-NH2)of the lectin domain of E-, L- and P-selectins, were analysedfor their ability to block selectin-mediated cell adhesion invitro, and neutrophil infiltration into sites of inflammationin vivo. The peptides inhibited the adhesion of myeloid cellsto recombinant forms of E- and P-selectin. The adhesion of myeloidcells to human endothelial cells, stimulated to express E-selectin,was also inhibited by the peptides. Finally, the peptides blockedthe adhesion of lymphocytes, expressing L-selectin, to highendothelial venules in lymph nodes which contain the ligandfor L-selectin. A clear structure-activity relationship wasestablished when peptides of different amino acid chain lengthswere tested in these assays. Peptides lacking tyrosine residues(e.g. WIGIR-NH2) at their amino terminus were poor inhibitorsof selectin-mediated cell adhesion in vitro. The peptides thatwere found to be inhibitors of cell adhesion in vitro were alsofound to inhibit (up to 70%) neutrophil infiltration into sitesof inflammation in a thioglycollate-induced peritonitis mousemodel system. They also significantly reduced (>50%) themigration of neutrophils into cytokine-treated skin. These resultsstrongly suggest that compounds based on these tyrosine-containing,selectin-derived peptides could be used as anti-inflammatorytherapeutic agents. inflammation neutrophils peptides selectins 相似文献
989.
990.
Genetic regulation of gibberellin deactivation in Pisum 总被引:2,自引:0,他引:2
John J. Ross James B. Reid Stephen M. Swain Omar Hasan rew T. Poole Peter Hedden Christine L. Willis 《The Plant journal : for cell and molecular biology》1995,7(3):513-523
The regulation of gibberellin (GA) deactivation was examined using the sin (slender) mutation in the garden pea (Pisum sativum L.). This mutation blocks the deactivation of GA20, the precursor of the bioactive GA1. Firstly, crosses were made to combine sin with the GA biosynthesis mutations na, lhi and le-3. The combination sin na produced a novel phenotype, with long (‘slender’) basal internodes and extremely short (‘nana’) upper internodes. In contrast, the double mutant sin lhi was phenotypically dwarf. The mutation sin causes an accumulation of GA20 in maturing seeds, and this was unaffected by na, since the na mutation is not expressed in seeds. In contrast, lhi seeds did not accumulate GA20, since lhi imposes an early block on GA biosynthesis. Secondly, the effects of sin on several steps in GA deactivation were investigated. In maturing seeds, the mutation sin blocks two steps in GA20 metabolism, namely, GA20 to GA29, and GA29 to GA29-catabolite. In the vegetative plant, on the other hand, sin blocked the step GA20 to GA29, but not GA29 to GA29-catabolite; the steps GA20 to GA81 and GA20 to GA1 were also not impaired in this mutant. It is clear that the effects of sin, like those of na, are strongly organ-specific. The presence of separate enzymes for the steps GA20 to GA29 and GA29 to GA29-catabolite was suggested by the observation that GA8 inhibited the latter step, but not the former, and by the inability of GA20 and GA29 to inhibit each other's metabolism. It is suggested that the Sin gene may be a regulatory gene controlling the expression of two structural genes involved in GA deactivation. 相似文献