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91.
Contiguous organization of nitrogenase genes in a heterocystous cyanobacterium 总被引:7,自引:0,他引:7 下载免费PDF全文
The organization of the three structural nitrogen fixation (nif) genes that encode nitrogenase (nif K and nif D) and nitrogenase reductase (nif H) have been examined in a number of cyanobacteria. Hybridization of Anabaena 7120 nif gene probes to restriction endonuclease-digested genomic DNA has shown (a) that cyanobacteria incapable of N2 fixation have no regions of DNA with significant homology to the three nif probes, (b) that Pseudanabaena sp., a nonheterocystous cyanobacterium, has a contiguous nif KDH gene cluster, and (c) that in contrast with other heterocystous cyanobacteria, Fischerella sp. has a contiguous nif KDH gene cluster. 相似文献
92.
OBJECTIVE: To determine whether women diagnosed with adenocarcinoma in situ (AIS) of the cervix are as well screened as healthy control women. STUDY DESIGN: A case-control study was performed (307 cases, 1,228 controls) within a statewide registry. Cases consisted of women diagnosed with AIS on histology between 1995 and 2001. Screening histories were compiled from registry records. Variables of interest included number of previous negative Pap smears, time interval since last negative Pap smear, median time between previous negative Pap smears, proportion of negative Pap smears with an endocervical component and history of cervical abnormality. RESULTS: Conditional logistic regression showed that cases and controls did not differ significantly in the number of previous negative smears or in the median time between previous negative smears. Decreasing time since last negative smear was protective against AIS, with controls more likely to have had a recent negative smear. There was no difference in the proportion of previous negative smears with an endocervical component between cases and controls; however, some complex temporal relationships were observed in the regression analysis. CONCLUSION: Women who are diagnosed with AIS have a screening history similar to that of healthy, control women. The findings are consistent with the concept that AIS is predominantly a screening-detected disease. 相似文献
93.
94.
Peripheral alpha1,3-fucosylation of glycans occurs by the action of either
one of five different alpha1,3-fucosyltransferases (Fuc-Ts) cloned to date.
Fuc-TVI is one of the alpha1,3-fucosyltransferases which is capable to
synthesize selectin ligands. The major alpha1, 3- fucosyltransferase
activity in human plasma is encoded by the gene for fucosyltransferase VI,
which presumably originates from liver cells. While the sequence,
chromosomal localization, and kinetic properties of Fuc-TVI are known,
immunocytochemical localization and trafficking studies have been
impossible because of the lack of specific antibodies. Here we report on
the development and characterization of a peptide-specific polyclonal
antiserum monospecific to Fuc-TVI and an antiserum to purified soluble
recombinant Fuc-TVI crossreactive with Fuc-TIII and Fuc-TV. Both antisera
were applied for immunodetection in stably transfected CHO cells expressing
the full-length form of this enzyme (CHO clone 61/11). Fuc-TVI was found to
be a resident protein of the Golgi apparatus. In addition, more than 30% of
cell-associated and released enzyme activity was found in the medium.
Maturation and release of Fuc-TVI was analyzed in metabolically labeled CHO
61/11 cells followed by immunoprecipitation. Fuc-TVI occurred in two forms
of 47 kDa and 43 kDa bands, while the secreted form was detected as a 43
kDa. These two different intracellular forms arose by posttranslational
modification, as shown by pulse-chase experiments. Fuc-TVI was released to
the supernatant by proteolytic cleavage as a partially endo-H resistant
glycoform.
相似文献
95.
Abstract: Intensive sampling of the Luolou (northwestern Guangxi) and the Daye (southern Guizhou) Formations in South China leads to the recognition of a regional Griesbachian and Dienerian ammonoid succession for this key palaeobiogeographical area. The new biostratigraphical sequence comprises the upper Griesbachian ‘Ophiceras beds’ and the lower Dienerian ‘Proptychites candidus beds’, which are separated from the uppermost Dienerian ‘Clypites beds’ by an unfossiliferous interval. These faunas contain some taxa with wide geographic distribution (e.g. Ambites, Pleurambites, Pleurogyronites, Proptychites candidus), thus facilitating correlation with faunal successions from other regions (i.e. British Columbia, Canadian Arctic, Himalayas and South Primorye). Two new genera (Jieshaniceras and Shangganites) and three new species (Anotoceras subtabulatus, Pleurambites radiatus and Shangganites shangganense) are described. 相似文献
96.
We analyzed the integration specificity of the hobo transposable element of Drosophila melanogaster. Our results indicate
that hobo is similar to other transposable elements in that it can integrate into a large number of sites, but that some sites
are preferred over others, with a few sites acting as integration hot spots. A comparison of DNA sequences from 112 hobo integration
sites identified a consensus sequence of NTNNNNAC, but this consensus was insufficient to account for the observed integration
specificity. To begin to define the parameters affecting hobo integration preferences, we analyzed sequences flanking a donor
hobo element, as well as sequences flanking a hobo integration hot spot for their relative influence on hobo integration specificity.
We demonstrate experimentally that sequences flanking a hobo donor element do not influence subsequent integration site preference,
whereas, sequences contained within 31 base pairs flanking an integration hot spot have a significant effect on the frequency
of integration into that site. However, sequence analysis of the DNA flanking several hot spots failed to identify any common
sequence motif shared by these sites. This lack of primary sequence information suggests that higher order DNA structural
characteristics of the DNA and/or chromatin may influence integration site selection by the hobo element.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
97.
98.
P. R. Saville 《BMJ (Clinical research ed.)》1957,1(5011):158-160
99.
Annual methane uptake by temperate semiarid steppes as regulated by stocking rates,aboveground plant biomass and topsoil air permeability 总被引:1,自引:0,他引:1
WEIWEI CHEN BENJAMIN WOLF XUNHUA ZHENG ZHISHENG YAO KLAUS BUTTERBACH‐BAHL NICOLAS BRÜGGEMANN CHUNYAN LIU SHENGHUI HAN XINGGUO HAN 《Global Change Biology》2011,17(9):2803-2816
Overgrazing‐induced degradation of temperate semiarid steppes may affect the soil sink for atmospheric methane (CH4). However, previous studies have primarily focused on the growing season and on single grazing patterns. Thus, the response of annual CH4 uptake by steppes compared with various grazing practices is uncertain. In this study, we investigated the effects of grazing on the annual CH4 uptake by two typical Eurasian semiarid steppes (the Stipa grandis steppe and the Leymus chinensis steppe) located in Inner Mongolia, China. The CH4 fluxes were measured year‐round using static chambers and gas chromatography at 12 field sites that differed primarily in grazing intensities. Our results indicated that steppe soils were CH4 sinks throughout the year. The annual CH4 uptake correlated with stocking rates, whereas the seasonality of CH4 uptake was primarily dominated by temperature. The annual CH4 uptake at all sites averaged 3.7±0.7 kg C ha?1 yr?1 (range: 2.3–4.5), where approximately 35% (range: 23–40%) occurred during the nongrowing season. Light‐to‐moderate grazing (stocking rate≤1 sheep ha?1 yr?1) did not significantly change the annual CH4 uptake compared with ungrazed steppes, but heavy grazing reduced annual CH4 uptake significantly (by 24–31%, P<0.05). These findings imply that easing the pressure of heavily grazed steppes (e.g. moving to light or moderate stocking rates) would help restore steppe soil sinks for atmospheric CH4. The empirical equations based on the significant relationships between annual CH4 uptake and stocking rates, aboveground plant biomass and topsoil air permeability (P<0.01) could provide simple approaches for the estimation of regional CH4 uptake by temperate semiarid steppes. 相似文献
100.