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121.
Pawel Drozdzal Miroslaw Gilski Mariusz Jaskolski 《Acta Crystallographica. Section D, Structural Biology》2016,72(11):1203-1211
The self‐complementary d(CGCGCG) hexanucleotide was synthesized with both d ‐2′‐deoxyribose (the natural enantiomer) and l ‐2′‐deoxyribose, and the two enantiomers were mixed in racemic (1:1) proportions and crystallized, producing a new crystal form with C2/c symmetry that diffracted X‐rays to 0.78 Å resolution. The structure was solved by direct, dual‐space and molecular‐replacement methods and was refined to an R factor of 13.86%. The asymmetric unit of the crystal contains one Z‐DNA duplex and three Mg2+ sites. The crystal structure is comprised of both left‐handed (d ‐form) and right‐handed (l ‐form) Z‐DNA duplexes and shows an unexpectedly high degree of structural disorder, which is manifested by the presence of alternate conformations along the DNA backbone chains as well as at four nucleobases (including one base pair) modelled in double conformations. The crystal packing of the presented d /l ‐DNA–Mg2+ structure exhibits novel DNA hydration patterns and an unusual arrangement of the DNA helices in the unit cell. The paper describes the structure in detail, concentrating on the mode of disorder, and compares the crystal packing of the racemic d(CGCGCG)2 duplex with those of other homochiral and heterochiral Z‐DNA structures. 相似文献
122.
Tobacco use leads to 6 million deaths every year due to severe long‐lasting diseases. The main component of tobacco, nicotine, is recognized as one of the most addictive drugs, making smoking cessation difficult, even when 70 percent of smokers wish to do so. Clinical and preclinical studies have demonstrated consistently that nicotine seeking is a complex behavior involving various psychopharmacological mechanisms. Evidence supports that the population of smokers is heterogeneous, particularly as regards the breadth of motives that determine the urge to smoke. Here, we review converging psychological, genetic and neurobiological data from clinical and preclinical studies supporting that the mechanisms controlling nicotine seeking may vary from individual to individual. It appears timely that basic neuroscience integrates this heterogeneity to refine our understanding of the neurobiology of nicotine seeking, as tremendous progress has been made in modeling the various psychopharmacological mechanisms driving nicotine seeking in rodents. For a better understanding of the mechanisms that drive nicotine seeking, we emphasize the need for individual‐based research strategies in which nicotine seeking, and eventually treatment efficacy, are determined while taking into account individual variations in the mechanisms of nicotine seeking. 相似文献
123.
Data on social organization of two bands of black-and-white snub-nosed monkeys (Rhinopithecus bieti) were collected when the monkeys were crossing an open spot at Nanren and Bamei (northwest of Yunnan, China) using a sampling rule where individuals within one social unit are spatially closer to each other than individuals between social units. The typical pattern of social organization in this sample was multiple adult females (AFs) and their offspring with one adult male (AM) in a one-male unit (OMU), similar to that of many other colobines. In such units, on average one male is associated with 4.0 AFs and 2.5 of their offspring. Moreover, there are multimale/multifemale units and monogamous units besides OMUs. All bisexual units traveled together with at least one all-male unit as a cohesive band. In two bands of monkeys, 87% of AMs in bisexual units were within OMUs, 7.8% within monogamous units and 5.2% within multimale, multifemale units. In the Bamei band, 6.7% of AMs were in the all-male unit. The size of OMUs in the Nanren band was larger than that of the Bamei band, with more AFs and juveniles, which may be related to better conservation in the Nanren band's habitat. For the Nanren band, the average number of AFs in OMUs varied across time, increasing from 4.3 in 1994 to 5.1 in 2001, and then decreasing to 3.8 in 2005. This article suggests three possible explanations for this variation, but more data are needed for these hypotheses to be tested. 相似文献
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With the molecular revolution in Biology, a mechanistic understanding of the genotype–phenotype relationship became possible. Recently, advances in DNA synthesis and sequencing have enabled the development of deep mutational scanning assays, capable of scoring comprehensive libraries of genotypes for fitness and a variety of phenotypes in massively parallel fashion. The resulting empirical genotype–fitness maps pave the way to predictive models, potentially accelerating our ability to anticipate the behaviour of pathogen and cancerous cell populations from sequencing data. Besides from cellular fitness, phenotypes of direct application in industry (e.g. enzyme activity) and medicine (e.g. antibody binding) can be quantified and even selected directly by these assays. This review discusses the technological basis of and recent developments in massively parallel genetics, along with the trends it is uncovering in the genotype–phenotype relationship (distribution of mutation effects, epistasis), their possible mechanistic bases and future directions for advancing towards the goal of predictive genetics. 相似文献
126.
Identifying the mechanisms underlying invasive plant establishment and native plant decline remains a central goal in ecology, particularly for biodiversity hotspots such as islands. We re‐analyzed a previously published meta‐dataset to test the prediction that neighbor effects are stronger on islands vs. continents because island plants are weaker competitors. Although we detected marginally stronger neighbor effects on islands than continents, this was due, at least in part, to stronger competition among native species. An absence of studies testing neighbor effects between native vs. invasive plants on islands prevents a rigorous test for competition effects on islands, highlighting an important knowledge gap. 相似文献
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129.
1. Insect oral secretions are important for the induction of a number of plant responses, but the relative role of mechanical damage in the induction of these responses is often not well understood. Damage from the frugivore Heliothis subflexa, a specialist on Physalis species, causes herbivore‐induced fruit abscission. In this field study, we examined the separate and combined effects of mechanical damage and H. subflexa oral secretions on Physalis fruit abscission. 2. To determine the relative role of mechanical and chemical factors, the following treatments were administered to fruit: (1) three levels of mechanical damage, (2) natural herbivore damage by control larvae and by larvae surgically treated to inhibit saliva secretion, and (3) injection of H.subflexa oral secretions and a water control. Abscission of mechanically damaged fruit with and without the addition of oral secretions was also compared. 3. Mechanical damage was sufficient to cause fruit abscission, and the addition of oral secretions to mechanically damaged fruit did not cause an increase in fruit abscission. Normal caterpillars and those treated to inhibit saliva secretion caused similar abscission rates. 4. Though most studies examining the effects of insect oral secretions on induced plant responses find these chemical stimuli to be important or essential, the results of the present study showed that oral secretions are not necessary for fruit abscission. Future work is needed to determine the relative importance of mechanical damage in herbivore‐induced plant responses in other systems. 相似文献
130.
Lucy A. Howey Emily R. Tolentino Yannis P. Papastamatiou Edward J. Brooks Debra L. Abercrombie Yuuki Y. Watanabe Sean Williams Annabelle Brooks Demian D. Chapman Lance K.B. Jordan 《Ecology and evolution》2016,6(15):5290-5304
Comprehension of ecological processes in marine animals requires information regarding dynamic vertical habitat use. While many pelagic predators primarily associate with epipelagic waters, some species routinely dive beyond the deep scattering layer. Actuation for exploiting these aphotic habitats remains largely unknown. Recent telemetry data from oceanic whitetip sharks (Carcharhinus longimanus) in the Atlantic show a strong association with warm waters (>20°C) less than 200 m. Yet, individuals regularly exhibit excursions into the meso‐ and bathypelagic zone. In order to examine deep‐diving behavior in oceanic whitetip sharks, we physically recovered 16 pop‐up satellite archival tags and analyzed the high‐resolution depth and temperature data. Diving behavior was evaluated in the context of plausible functional behavior hypotheses including interactive behaviors, energy conservation, thermoregulation, navigation, and foraging. Mesopelagic excursions (n = 610) occurred throughout the entire migratory circuit in all individuals, with no indication of site specificity. Six depth‐versus‐time descent and ascent profiles were identified. Descent profile shapes showed little association with examined environmental variables. Contrastingly, ascent profile shapes were related to environmental factors and appear to represent unique behavioral responses to abiotic conditions present at the dive apex. However, environmental conditions may not be the sole factors influencing ascents, as ascent mode may be linked to intentional behaviors. While dive functionality remains unconfirmed, our study suggests that mesopelagic excursions relate to active foraging behavior or navigation. Dive timing, prey constituents, and dive shape support foraging as the most viable hypothesis for mesopelagic excursions, indicating that the oceanic whitetip shark may regularly survey extreme environments (deep depths, low temperatures) as a foraging strategy. At the apex of these deep‐water excursions, sharks exhibit a variable behavioral response, perhaps, indicating the presence or absence of prey. 相似文献