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991.
992.
Marijn T. J. van Loenhout Thijn van der Heijden Roland Kanaar Claire Wyman Cees Dekker 《Nucleic acids research》2009,37(12):4089-4099
RecA, the key protein in homologous recombination, performs its actions as a helical filament on single-stranded DNA (ssDNA). ATP hydrolysis makes the RecA–ssDNA filament dynamic and is essential for successful recombination. RecA has been studied extensively by single-molecule techniques on double-stranded DNA (dsDNA). Here we directly probe the structure and kinetics of RecA interaction with its biologically most relevant substrate, long ssDNA molecules. We find that RecA ATPase activity is required for the formation of long continuous filaments on ssDNA. These filaments both nucleate and extend with a multimeric unit as indicated by the Hill coefficient of 5.4 for filament nucleation. Disassembly rates of RecA from ssDNA decrease with applied stretching force, corresponding to a mechanism where protein-induced stretching of the ssDNA aids in the disassembly. Finally, we show that RecA–ssDNA filaments can reversibly interconvert between an extended, ATP-bound, and a compressed, ADP-bound state. Taken together, our results demonstrate that ATP hydrolysis has a major influence on the structure and state of RecA filaments on ssDNA. 相似文献
993.
Christine A. Caldwell Claire F.E. Watson Keith D. Morris 《Applied animal behaviour science》2009,116(2-4):244-249
Although commercially available complete diets exist for common marmosets, the animals’ consumption of these diets (available in dry pellet form) is typically very low. Increasing consumption of the pellet diet could have positive consequences for the welfare of the marmosets as the pellets are designed specifically to meet their full nutritional requirements, and therefore an increase in intake should help to ensure that they take in an appropriate balance of nutrients. We carried out a series of studies targeted towards improving the palatability, and hence increasing the intake, of a complete dry pellet diet for marmosets. In Study 1 we attempted to determine which of a wide range of flavours appeared to be preferred by the marmosets. In Study 2 we tested the marmosets’ preferences for a smaller number of highly preferred flavours (as determined in Study 1) when actually added to the dry pellet diet in a series of paired preference tests. Finally, in Study 3 we tested whether adding the most highly preferred flavours (as determined in Study 2) to the dry pellet diet would in fact increase consumption of these pellets in comparison with unflavoured pellets. Despite finding strong and consistent preferences for particular flavours amongst the marmosets, we found that adding these to the pellets did not significantly increase consumption. Reasons for this are discussed, along with other potential modifications which might prove more successful in increasing consumption of pellet diets for marmosets. 相似文献
994.
Siobhan M. Abeyesinghe Morven A. McLeman Rachael C. Owen Claire E. McMahon Christopher M. Wathes 《Behavioural processes》2009,81(1):1-13
Social relationships in domestic fowl are commonly assumed to rely on social recognition and its pre-requisite, discrimination of group-mates. If this is true, then the unnatural physical and social environments in which commercial laying hens are typically housed, when compared with those in which their progenitor species evolved, may compromise social function with consequent implications for welfare. Our aims were to determine whether adult hens can discriminate between unique pairs of familiar conspecifics, and to establish the most appropriate method for assessing this social discrimination. We investigated group-mate discrimination using two learning tasks in which there was bi-directional exchange of visual, auditory and olfactory information. Learning occurred in a Y-maze task (p < 0.003; n = 7/8) but not in an operant key-pecking task (p = 0.001; n = 1/10). A further experiment with the operant-trained hens examined whether failure was specific to the group-mate social discrimination or to the response task. Learning also failed to occur in this familiar/unfamiliar social discrimination task (p = 0.001; n = 1/10). Our findings demonstrate unequivocally that adult laying hens kept in small groups, under environmental conditions more consistent with those in which sensory capacities evolved, can discriminate group members: however, appropriate methods to demonstrate discrimination are crucial. 相似文献
995.
Difference in number of loci of swine leukocyte antigen classical class I genes among haplotypes 总被引:1,自引:0,他引:1
The structure of the entire genomic region of swine leukocyte antigen (SLA)-the porcine major histocompatibility complex--was recently elucidated in a particular haplotype named Hp-1.0 (H01). However, it has been suggested that there are differences in the number of loci of SLA genes, particularly classical class I genes, among haplotypes. To clarify the between-haplotype copy number variance in genes of the SLA region, we sequenced the genomic region carrying SLA classical class I genes on two different haplotypes, revealing increments of up to six in the number of classical class I genes in a single haplotype. All of the SLA-1(-like) (SLA-1 and newly designated SLA-12) and SLA-3 genes detected in the haplotypes thus analyzed were transcribed in the individual. The process by which duplication of SLA classical class I genes was likely to have occurred was interpreted from an analysis of repetitive sequences adjacent to the duplicated class I genes. 相似文献
996.
Delayed fluorescence as a universal tool for the measurement of circadian rhythms in higher plants 总被引:1,自引:0,他引:1
Peter D. Gould Patrick Diaz Claire Hogben Jelena Kusakina Radia Salem James Hartwell Anthony Hall 《The Plant journal : for cell and molecular biology》2009,58(5):893-901
The plant circadian clock plays an important role in enhancing performance and increasing vegetative yield. Much of our current understanding of the mechanism and function of the plant clock has come from the development of Arabidopsis thaliana as a model circadian organism. Key to this rapid progress has been the development of robust circadian markers, specifically circadian-regulated luciferase reporter genes. Studies of the clock in crop species and non-model organisms are currently hindered by the absence of a simple high-throughput universal assay for clock function, accuracy and robustness. Delayed fluorescence (DF) is a fundamental process occurring in all photosynthetic organisms. It is luminescence-produced post-illumination due to charge recombination in photosystem II (PSII) leading to excitation of P680 and the subsequent emission of a photon. Here we report that the amount of DF oscillates with an approximately 24-h period and is under the control of the circadian clock in a diverse selection of plants. Thus, DF provides a simple clock output that may allow the clock to be assayed in vivo in any photosynthetic organism. Furthermore, our data provide direct evidence that the nucleus-encoded, three-loop circadian oscillator underlies rhythms of PSII activity in the chloroplast. This simple, high-throughput and non-transgenic assay could be integrated into crop breeding programmes, the assay allows the selection of plants that have robust and accurate clocks, and possibly enhanced performance and vegetative yield. This assay could also be used to characterize rapidly the role and function of any novel Arabidopsis circadian mutant. 相似文献
997.
998.
Nico Dissmeyer Annika K. Weimer Stefan Pusch Kristof De Schutter Claire Lessa Alvim Kamei Moritz K. Nowack Bela Novak Gui-Lan Duan Yong-Guan Zhu Lieven De Veylder Arp Schnittger 《The Plant cell》2009,21(11):3641-3654
Entry into mitosis is universally controlled by cyclin-dependent kinases (CDKs). A key regulatory event in metazoans and fission yeast is CDK activation by the removal of inhibitory phosphate groups in the ATP binding pocket catalyzed by Cdc25 phosphatases. In contrast with other multicellular organisms, we show here that in the flowering plant Arabidopsis thaliana, cell cycle control does not depend on sudden changes in the phosphorylation pattern of the PSTAIRE-containing Cdk1 homolog CDKA;1. Consistently, we found that neither mutants in a previously identified CDC25 candidate gene nor plants in which it is overexpressed display cell cycle defects. Inhibitory phosphorylation of CDKs is also the key event in metazoans to arrest cell cycle progression upon DNA damage. However, we show here that the DNA damage checkpoint in Arabidopsis can also operate independently of the phosphorylation of CDKA;1. These observations reveal a surprising degree of divergence in the circuitry of highly conserved core cell cycle regulators in multicellular organisms. Based on biomathematical simulations, we propose a plant-specific model of how progression through the cell cycle could be wired in Arabidopsis. 相似文献
999.
Margaret P. Donaldson Kevin J. Edwards Andrew A. Meharg Claire Deacon Donald A. Davidson 《Review of Palaeobotany and Palynology》2009,153(1-2):46-61
This paper presents findings based on a palynological investigation of artificially accreting (plaggen) soils from the settlement of Village Bay, Hirta, in the St Kilda archipelago, which was perhaps the most distant and inhospitable outpost of sustained human habitation in the British Isles. The soils were developed principally through the addition of turf ash and seabird waste, although some ash may have been derived from upland peats. It is assumed that the woodland pollen signal (much lower in the soils than in an upland peat site nearby) represents off-island sources. Corylus avellana-type pollen (frequent in upland sites), along with Potentilla-type, may provide markers in the Village Bay profiles for the addition of ashed hillside turf, and possibly peat, to the plaggen soils. Cereal-type pollen is well represented through the profiles and is often strongly associated with the record for Chrysanthemum segetum (corn marigold), a frequent indicator of arable land. The Brassicaceae signal may partly reflect the cultivation of cabbages; Chelidonium majus (greater celandine) may have been grown for medicinal use. Soil mixing has rendered radiocarbon dating meaningless at this site, but the establishment of a change in cultivation regime before AD 1830 may have been identified from the patterns of pollen concentration and preservation in the profiles. 相似文献