Fluorescence-force spectroscopy maps two-dimensional reaction landscape of the holliday junction     

Hohng S  Zhou R  Nahas MK  Yu J  Schulten K  Lilley DM  Ha T 《Science (New York, N.Y.)》2007,318(5848):279-283

Despite the recent advances in single-molecule manipulation techniques, purely mechanical approaches cannot detect subtle conformational changes in the biologically important regime of weak forces. We developed a hybrid scheme combining force and fluorescence that allowed us to examine the effect of subpiconewton forces on the nanometer scale motion of the Holliday junction (HJ) at 100-hertz bandwidth. The HJ is an exquisitely sensitive force sensor whose force response is amplified with an increase in its arm lengths, demonstrating a lever-arm effect at the nanometer-length scale. Mechanical interrogation of the HJ in three different directions helped elucidate the structures of the transient species populated during its conformational changes. This method of mapping two-dimensional reaction landscapes at low forces is readily applicable to other nucleic acid systems and their interactions with proteins and enzymes.  相似文献   

White fat progenitor cells reside in the adipose vasculature   总被引：1，自引：0，他引：1  

Tang W  Zeve D  Suh JM  Bosnakovski D  Kyba M  Hammer RE  Tallquist MD  Graff JM 《Science (New York, N.Y.)》2008,322(5901):583-586

White adipose (fat) tissues regulate metabolism, reproduction, and life span. Adipocytes form throughout life, with the most marked expansion of the lineage occurring during the postnatal period. Adipocytes develop in coordination with the vasculature, but the identity and location of white adipocyte progenitor cells in vivo are unknown. We used genetically marked mice to isolate proliferating and renewing adipogenic progenitors. We found that most adipocytes descend from a pool of these proliferating progenitors that are already committed, either prenatally or early in postnatal life. These progenitors reside in the mural cell compartment of the adipose vasculature, but not in the vasculature of other tissues. Thus, the adipose vasculature appears to function as a progenitor niche and may provide signals for adipocyte development.  相似文献   

Genetics. DNA patenting and licensing     

Henry MR  Cho MK  Weaver MA  Merz JF 《Science (New York, N.Y.)》2002,297(5585):1279

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Orangutan cultures and the evolution of material culture     

van Schaik CP  Ancrenaz M  Borgen G  Galdikas B  Knott CD  Singleton I  Suzuki A  Utami SS  Merrill M 《Science (New York, N.Y.)》2003,299(5603):102-105

Geographic variation in some aspects of chimpanzee behavior has been interpreted as evidence for culture. Here we document similar geographic variation in orangutan behaviors. Moreover, as expected under a cultural interpretation, we find a correlation between geographic distance and cultural difference, a correlation between the abundance of opportunities for social learning and the size of the local cultural repertoire, and no effect of habitat on the content of culture. Hence, great-ape cultures exist, and may have done so for at least 14 million years.  相似文献   

Environmental economics. Development and conservation goals in World Bank projects     

Kareiva P  Chang A  Marvier M 《Science (New York, N.Y.)》2008,321(5896):1638-1639

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Stochastic pulse regulation in bacterial stress response     

Locke JC  Young JW  Fontes M  Hernández Jiménez MJ  Elowitz MB 《Science (New York, N.Y.)》2011,334(6054):366-369

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Graduate students' teaching experiences improve their methodological research skills     

Feldon DF  Peugh J  Timmerman BE  Maher MA  Hurst M  Strickland D  Gilmore JA  Stiegelmeyer C 《Science (New York, N.Y.)》2011,333(6045):1037-1039

Science, technology, engineering, and mathematics (STEM) graduate students are often encouraged to maximize their engagement with supervised research and minimize teaching obligations. However, the process of teaching students engaged in inquiry provides practice in the application of important research skills. Using a performance rubric, we compared the quality of methodological skills demonstrated in written research proposals for two groups of early career graduate students (those with both teaching and research responsibilities and those with only research responsibilities) at the beginning and end of an academic year. After statistically controlling for preexisting differences between groups, students who both taught and conducted research demonstrate significantly greater improvement in their abilities to generate testable hypotheses and design valid experiments. These results indicate that teaching experience can contribute substantially to the improvement of essential research skills.  相似文献   

Terraces in phylogenetic tree space     

Sanderson MJ  McMahon MM  Steel M 《Science (New York, N.Y.)》2011,333(6041):448-450

A key step in assembling the tree of life is the construction of species-rich phylogenies from multilocus--but often incomplete--sequence data sets. We describe previously unknown structure in the landscape of solutions to the tree reconstruction problem, comprising sometimes vast "terraces" of trees with identical quality, arranged on islands of phylogenetically similar trees. Phylogenetic ambiguity within a terrace can be characterized efficiently and then ameliorated by new algorithms for obtaining a terrace's maximum-agreement subtree or by identifying the smallest set of new targets for additional sequencing. Algorithms to find optimal trees or estimate Bayesian posterior tree distributions may need to navigate strategically in the neighborhood of large terraces in tree space.  相似文献   

Effect of dextransucrase cellobiose acceptor products on the growth of human gut bacteria     

Ruiz-Matute AI  Brokl M  Sanz ML  Soria AC  Côté GL  Collins ME  Rastall RA 《Journal of agricultural and food chemistry》2011,59(8):3693-3700

The selective fermentation by human gut bacteria of gluco-oligosaccharides obtained from the reaction between the glucosyl group of sucrose and cellobiose, catalyzed by dextransucrases (DSR) from Leuconostoc mesenteroides , has been evaluated. Oligosaccharides were fractionated according to their molecular weight, and their effect on the growth of different bacterial groups was studied. To determine the structure (position and configuration of glycosidic linkages)-function relationship, their properties were compared to those of DSR maltose acceptor products (DSRMal) and of recognized prebiotic carbohydrates (fructo-oligosaccharides, FOS). Cellobiose acceptor products (DSRCel) showed bifidogenic properties similar to those of FOS. However, no significant differences related to molecular weight or isomeric configurations were found for DSRCel and DSRMal products.  相似文献   

Evaluation of modified techniques for immobilization of wild ring-tailed lemurs (Lemur catta)     

Larsen RS  Sauther ML  Cuozzo FP 《Journal of zoo and wildlife medicine》2011,42(4):623-633

Wild ring-tailed lemurs (Lemur catta) can be anesthetized with Telazol via blow dart, but improved techniques are needed so that each lemur is reliably induced with a single dart. Medetomidine-butorphanol (MB) is a good supplemental protocol to be administered once the lemurs are captured, but other protocols may provide longer periods of sedation and immobility. One possible way of increasing the efficacy of each dart is to increase the time it is retained in the leg. In this investigation, a "double-sleeve" technique was used to try to increase the time of dart retention. This technique used a standard silicone sleeve on the needle, along with a second sleeve at the needle hub. Induction values were compared between lemurs darted with double-sleeve needles and those induced with needles that each had a single silicone sleeve. Once the lemurs were induced, supplementation with MB (0.04 mg/kg and 0.2 mg/kg) was compared with supplementation with ketamine-medetomidine (KM) (10 mg/ kg and 0.04 mg/kg). Twenty-three lemurs were darted with Telazol by using single-sleeve needles, and 24 were darted with double-sleeve needles. The number of darts per lemur and number of escapes were not different between animals darted with a single sleeve compared with a double-sleeve; thus, there were no significant improvements in induction success with the double-sleeve technique. Adequate sedation and muscle relaxation were achieved with both MB and KM; however, lemurs that received MB were more relaxed and needed fewer additional supplements that those that received KM. Single-sleeve dart needles are recommended for Telazol induction of ring-tailed lemurs via blow dart and MB is preferable to KM for supplemental sedation and muscle relaxation.  相似文献