共查询到20条相似文献,搜索用时 0 毫秒
1.
2.
3.
Restriction endonucleases can be used to study B-Z junctions in supercoiled DNA. 总被引:13,自引:1,他引:12
下载免费PDF全文
![点击此处可从《Proceedings of the National Academy of Sciences of the United States of America》网站下载免费的PDF全文](/ch/ext_images/free.gif)
F Azorin R Hahn A Rich 《Proceedings of the National Academy of Sciences of the United States of America》1984,81(18):5714-5718
Plasmids containing (C-G)n inserts have been used to study the inhibition of cleavage by restriction endonucleases due to Z-DNA formation in negatively supercoiled plasmids. The enzyme BssHII, which recognizes G-C-G-C-G-C, is strongly inhibited when the insert forms Z-DNA. The BamHI recognition sequence (G-G-A-T-C-C) was placed in four different positions near the B-Z junction and the inhibition of BamHI cleavage was determined as a function of negative superhelical density. Formation of Z-DNA in the (C-G)n insert inhibited cleavage by BamHI when its recognition sequence was located immediately adjacent to the insert or four base pairs away from it. However, no inhibition was found when the BamHI recognition site was eight base pairs away. These experiments help to define the limits of the structural perturbation associated with the B-Z junction. 相似文献
4.
5.
T G Wegmann C A Waters D W Drell G A Carlson 《Proceedings of the National Academy of Sciences of the United States of America》1979,76(5):2410-2414
In this report we present evidence gathered from various stages of murine pregnancy that indicates that pregnant females have no demonstrable immune effector function directed against their semiallogeneic fetuses. Specifically, by using in vitro assays we found that cytotoxic lymphocytes were not present in pregnant mice, and pregnant mice challenged with radiolabeled paternal strain leukemia cells showed no evidence of immune elimination. Nonetheless, immunity measurable both in vitro and in vivo was readily induced by priming with the paternal strain cells. No harm to the fetus was observed in primed mothers. These results cast doubt on the relevance of mechanisms proposed that involve systemic active suppression during pregnancy. The results are compatible with the hypothesis that the placenta acts as a barrier, preventing fetal cells from priming the mother. 相似文献
6.
A M Vlieger G J Boland N M Jiwa R A de Weger R Willemze G C de Gast J H Falkenburg 《Bone marrow transplantation》1992,9(4):247-253
The antigenemia assay, polymerase chain reaction (PCR) and rapid culture technique on buffy coat cells (DEAFF test) were used to monitor 37 cytomegalovirus (CMV) seropositive bone marrow transplant (BMT) recipients for active CMV infection during the first 3 months after BMT. The antigen assay and PCR demonstrated a comparable sensitivity for the detection of CMV in blood: discordant results were only obtained in the early or late phase of infection when the viral load was low. The antigen assay was more sensitive than the DEAFF test. Only 12 out of 40 antigen-positive samples yielded a positive result with DEAFF test, whereas viremia without antigenemia was never found. The discordance between these two tests increased further during antiviral therapy with ganciclovir. A correlation was observed between the duration of antigenemia during treatment and the recurrence of systemic CMV reactivation. Ten out of 11 patients with antigen-positive leukocytes present for more than 1 week after starting the treatment subsequently exhibited a relapse of active infection, whereas only three out of nine patients who resolved their antigenemia within 1 week did so. In conclusion, the antigen assay and PCR are useful techniques for detection of CMV infection in BMT patients. Test results obtained during therapy give reliable information regarding the viral load and the possibility of recurrence of antigenemia, and can be taken into account when prolonged administration of ganciclovir is considered. 相似文献
7.
The activated clotting time (ACT) can be used to monitor enoxaparin and dalteparin after intravenous administration 总被引:4,自引:0,他引:4
BACKGROUND: The use of low-molecular weight heparin (LMWH) during percutaneous coronary intervention (PCI) has been limited by the presumed inability to monitor its anticoagulant effect using bedside assays. OBJECTIVES: This study was designed to compare the dose-response of enoxaparin, dalteparin and unfractionated heparin (UFH) on the activated clotting time (ACT), and to determine whether the ACT or aPTT can be used to monitor intravenous (IV) low molecular weight heparin (LMWH). METHODS: A total of 130 patients undergoing cardiac catheterization were assigned to intravenous enoxaparin 0.5 mg/kg, dalteparin 50 international units/kg or UFH 50 units/kg. Of the 130 patients, 46 (35%) underwent PCI, all of whom received a glycoprotein (GP) IIb/IIIa inhibitor. We measured ACT, activated partial thromboplastin time (aPTT) and plasma anti-Xa levels after serial sampling. RESULTS: Both enoxaparin and dalteparin induced a significant rise in the ACT and aPTT, with an ACT dose-response approximately one-half the magnitude of that obtained using UFH. The time course of changes in the ACT and aPTT after administration of enoxaparin and dalteparin was virtually identical, with a return to baseline at approximately 2 hours. The enoxaparin and dalteparin-treated patients successfully underwent PCI with no major hemorrhagic complications. CONCLUSIONS: The ACT is equally sensitive to IV enoxaparin and dalteparin. These data support an ACT-guided strategy for intravenously administered LMWH during PCI. Additional studies with larger patient populations may be indicated to determine the ideal target ACT for LMWH in PCI. 相似文献
8.
The activated clotting time can be used to monitor the low molecular weight heparin dalteparin after intravenous administration 总被引:6,自引:0,他引:6
Marmur JD Anand SX Bagga RS Fareed J Pan CM Sharma SK Richard MF 《Journal of the American College of Cardiology》2003,41(3):394-402
OBJECTIVES: This study was designed to compare the dose response of dalteparin versus unfractionated heparin (UFH) on the activated clotting time (ACT), and to determine whether the ACT can be used to monitor intravenous (IV) dalteparin during percutaneous coronary intervention (PCI). BACKGROUND: The use of low molecular weight heparin (LMWH) during PCI has been limited by the presumed inability to monitor its anticoagulant effect using bedside assays. METHODS: This study was performed in three phases. In vitro, ACTs were measured on volunteer (n = 10) blood samples spiked with increasing concentrations of dalteparin or UFH. To extend these observations in vivo, ACTs were then measured in patients (n = 15) who were sequentially treated with IV dalteparin and then UFH. Finally, a larger monitoring study was undertaken involving patients (n = 110) who received dalteparin 60 or 80 international U (IU)/kg alone or followed by abciximab. We measured ACT (Hemochron), activated partial thromboplastin time (aPTT), plasma anti-Xa and anti-IIa levels, tissue factor pathway inhibitor (TFPI) concentration, and plasma dalteparin concentration. RESULTS: Dalteparin induced a significant rise in the ACT with a smaller degree of variance as compared to UFH. Five min after administration of IV dalteparin 80 IU/kg the ACT increased from 125 s (122 s, 129 s) to 184 s (176 s, 191 s) (p < 0.001). The aPTT, anti-Xa and anti-IIa activities, and TFPI concentration also demonstrated significant increases following IV dalteparin. CONCLUSIONS: The ACT and aPTT are sensitive to IV dalteparin at clinically relevant doses. These data suggest that the ACT may be useful in monitoring the anticoagulant effect of intravenously administered dalteparin during PCI. 相似文献
9.
10.
11.
Ken Chen Hong Zhang Li-Na Zhang Shao-Qing Ju Jing Qi Dong-Feng Huang Feng Li Qun Wei Jing Zhang 《World journal of gastroenterology : WJG》2013,19(20):3143-3149
AIM:To investigate the value of combined detection of circulating cell-free DNA(cfDNA),a-fetal protein(AFP) and a L-fucosidase(AFU) for diagnosis of hepatocellular carcinoma(HCC).METHODS:Serum samples from 39 HCC patients and 45 normal controls were collected.Branched DNA(bDNA) was used to detect the level of cfDNA,and a receiver operating characteristic curve was employed to evaluate the diagnostic sensitivity,specificity,accuracy,positive predictive value,negative predictive value,positive likelihood ratio,negative likelihood ratio and Youden index,and to assess the diagnostic efficiency and their correlations with the clinicopathological features.AFP and AFU were detected by chemiluminescence and colorimetry,respectively.The significance of combined detection of the three biomarkers was discussed.RESULTS:cfDNA level was increased in 22 of the 39 HCC samples and in 2 of the 45 normal controls.cfDNA level in HCC samples was significantly higher than that in normal controls(P < 0.05).There were significant differences in sex and extra-and intrahepatic metastasis(P < 0.05).There was no significant correlation between cfDNA,AFP and AFU in the detection of HCC.The sensitivity of combined detection of cfDNA with one marker(AFP or AFU) and cfDNA with two markers(AFP and AFU) was 71.8%,87.2% and 89.7% vs 56.4%,53.8% and 66.7% for cfDNA,AFP and AFU used alone,respectively,the difference being statistically significant(P < 0.05).CONCLUSION:Quantitative analysis of cfDNA is sensitive and feasible,and the combined detection of cfDNA with AFP or AFU or both could improve the diagnostic sensitivity for HCC. 相似文献
12.
13.
Stefan Meyer Paulo Santos Fue Yang 《Proceedings of the National Academy of Sciences of the United States of America》2021,118(47)
We present experimental evidence of the impact of playing a game on real-life cooperation. The game was framed as a pest-management activity, the effectiveness of which depends on the decisions of others. Playing the game changes behavior in the field, increasing the participation in all collective activities directed at reducing pest pressure. The economic impact of those activities is important, leading to losses that are ∼20% lower than in the control group. Increased cooperation reflects changes in the understanding of others’ willingness to cooperate, not changes in the understanding of underlying technological interdependencies.Cooperation with nonkin is a distinctive aspect of human life (1), maintained by norms of conditional behavior (2), where norms have the accepted definition of shared views of how individuals ought to behave in a given situation (3). Promoting and sustaining cooperation in a context where it hitherto did not exist may require the elimination of inaccurate beliefs about others’ actions and beliefs, i.e., overcoming pluralistic ignorance (4).A variety of approaches have been used to create belief shocks that may lead to changes in behavioral norms (5–7). Changing the law (8) may provide an indication of the acceptability of some practices and foster changes in behavior (9) or perceptions (10). Similarly, “edutainment ” through radio shows (11), soap operas (12), or movies (13) can provide new role models that motivate the adoption of behaviors that were privately desired, but perceived as publicly shunned. At a local scale, information about what others do or value has been shown to promote environmental conservation (14), reduce alcohol consumption among teenagers (15), or increase female labor participation (16).In this paper, we evaluate the feasibility of using a framed game as an approach to promote cooperation. Similar to social scientists (17) or students in a classroom (18), participants in these games may learn about others’ behavior in conditions that were hitherto-unobserved, including about others’ willingness to cooperate (thereby reducing pluralistic ignorance), without having to incur the costs of promoting it themselves. This possibility was first noticed by ref. 19, and, building on that suggestion, recent work has used economic games as a teaching tool about the potential benefits of cooperation, usually in contexts where such problems are relatively new, such as the overexploitation of aquifers due to expanded access to water pumps (20–22). We build on this work in two ways: by experimentally evaluating the impact of playing a game on behavior outside the laboratory (improving on earlier evidence that mostly relies on a before–after comparison) and by quantifying the relative importance of reducing ignorance about others’ willingness to cooperate.The game was framed as a way of reducing rodent damage to rice. In Asia, such damage has important impacts on food security (23), which are particularly noticeable during outbreaks, some of which have even been followed by famine and civil unrest (24). Given the long history of association between rodents and humans (25, 26), the importance and persistence of such large losses is usually traced to rodents’ reproductive behavior, in particular, high litter size, short gestation period, and early sexual maturity (27, 28). In the absence of coordinated control (either by limiting rodents’ access to food and/or culling rodents), rodents quickly multiply, rendering any individual effort almost useless. This is certainly the case of the black rat (Rattus rattus), one of the main rodent pest species in the world (29), including in northern Lao People’s Democratic Republic (PDR), the setting of our analysis (30). The challenge, then, is how to coordinate multiple farmers into practicing rodent control over an extended period of time, when there are incentives to free-ride on others’ efforts to reduce pest pressure (27, 28), a problem common to the management of other pests and invasive species (31, 32).The game simulates this coordination problem in a simplified way. Players have to decide whether to contribute to reduce pest pressure by deciding how much time to allocate to the production of a private good (rice), knowing that the payoff (shown in 28)]. Still focusing on symmetric strategies, the social optimum can also be achieved with higher contributions (own contribution = {2, 3}), although these strategies do not correspond to a Nash equilibrium. Details about the rules of the game, as well as a discussion of players’ behavior, are presented in Methods.Table 1.Time allocation and payoff table (excerpt)
Open in a separate windowNote: Values are in LAK (1 USD = 8,650 LAK in May 2018). OT, others’ time contribution. Number of players = 5.The game was played as part of a project aimed at evaluating effective ways to promote food security implemented in 36 villages in Viengkham and Pakxeng, two districts in the province of Luang Prabang in northern Lao PDR. Data were collected among 12 households per village randomly selected from village rosters in November 2017 (baseline data) and December 2018 (when endline data were collected), with one additional survey collected in May 2018 (at the start of the main rice-producing season and immediately before the game was played). The baseline data confirm the importance of rodent damage in the region, a generalized awareness of interdependency in terms of the effect of individual decisions regarding rodent control has on neighbors’ production, and an absence of collective activities directed at reducing this problem. Almost all respondents (95%) reported that rodent damage is one of the main reasons that they harvested an area smaller than planted. Estimates of the damage are large and similar to earlier studies (30): On average, 20% of the planted area during the rainy season is not harvested due to rodent damage. Almost 90% of the respondents agree that they benefit from neighbors’ efforts at controlling rodents, but control mostly relies on individual use of traps (90% of the respondents) with no experience of coordinated control of this pest.Half of the villages participating in this study were randomly allocated to treatment (play the game), while the remaining were used as control. In each of the treatment villages, five groups of five players participated in the game. We first invited members of households who were previously interviewed (at baseline and then reinterviewed in May 2018, up to 12 participants per village, but usually less due to attrition), after which we invited members of other households randomly selected from the village roster to complete the desired number of participants per village. In total, 450 people participated in these games, of which 175 had been interviewed previously.In June 2018, all 36 villages received a short training on rodent control, delivered by local extension officers and focused on the implementation of collective rodent hunts (28), allowing them to overcome any limitation in the capacity to implement this approach. The training included a demonstration of how to implement collective hunting, with extension officers organizing one in each village in July 2018, after which villagers were encouraged to further organize these activities by themselves. Extension officers also pointed out that August and September would be the ideal times for further activities.The hypothesis we want to test is whether playing the game leads to changes in cooperation in the field during the forthcoming production season and, ultimately, to a reduction in area damaged by rodents. In addition, we want to understand the mechanisms that drive any change in behavior, distinguishing between learning about the benefits of collective action [usually emphasized in previous work (20, 21)] and learning about other players’ willingness to cooperate.Our identification strategy relies on the random allocation of treatment across villages. Randomization of treatment status was largely successful in creating two groups that are statistically identical at baseline. Similarly, selective attrition does not seem to be important. Training (0/1) Hunting (training) (0/1) Hunting (village) (0/1) Damage (% area) Community activities (d) A: ITT estimates, no covariates ITT 0.088 0.095* 0.098 –3.632** –0.149 SE (0.063) (0.050) (0.069) (1.689) (0.687) Wild-BS [0.181] [0.072] [0.174] [0.039] [0.824] B: ITT estimates, with covariates ITT 0.090* 0.097** 0.106* –3.542** 0.057 SE (0.053) (0.042) (0.061) (1.735) (0.637) Wild-BS [0.115] [0.042] [0.123] [0.056] [0.937] Control mean 0.662 0.508 0.344 18.772 5.651 N 399 399 399 344 346
OT | Your time – rodent control | |||||||
0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | |
0 | 7,000 | 7,000 | 7,000 | 6,500 | 5,500 | 4,500 | 3,500 | 2,500 |
1 | 7,500 | 7,000 | 7,000 | 6,500 | 5,500 | 5,000 | 3,500 | 2,500 |
2 | 7,500 | 7,500 | 7,000 | 6,500 | 6,000 | 5,000 | 4,000 | 2,500 |
3 | 7,500 | 7,500 | 7,000 | 6,500 | 6,000 | 5,000 | 4,000 | 2,500 |
4 | 7,500 | 7,500 | 7,000 | 6,500 | 6,000 | 5,000 | 4,000 | 2,500 |
5 | 7,500 | 7,500 | 7,500 | 7,000 | 6,000 | 5,000 | 4,000 | 3,000 |
6 | 8,000 | 7,500 | 7,500 | 7,000 | 6,000 | 5,500 | 4,000 | 3,000 |
7 | 8,000 | 8,000 | 7,500 | 7,000 | 6,500 | 5,500 | 4,500 | 3,000 |
8 | 8,000 | 8,000 | 7,500 | 7,000 | 6,500 | 5,500 | 4,500 | 3,000 |
9 | 8,000 | 8,000 | 7,500 | 7,000 | 6,500 | 5,500 | 4,500 | 3,000 |
10 | 8,000 | 8,000 | 8,000 | 7,500 | 6,500 | 5,500 | 4,500 | 3,500 |
11 | 8,500 | 8,000 | 8,000 | 7,500 | 6,500 | 6,000 | 4,500 | 3,500 |
12 | 8,500 | 8,500 | 8,000 | 7,500 | 7,000 | 6,000 | 5,000 | 3,500 |
13 | 8,500 | 8,500 | 8,000 | 7,500 | 7,000 | 6,000 | 5,000 | 3,500 |
26 | 10,000 | 9,500 | 9,500 | 9,000 | 8,000 | 7,500 | 6,000 | 5,000 |
27 | 10,000 | 10,000 | 9,500 | 9,000 | 8,500 | 7,500 | 6,500 | 5,000 |
28 | 10,000 | 10,000 | 9,500 | 9,000 | 8,500 | 7,500 | 6,500 | 5,000 |