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291.
RecA protein of Escherichia coli and chromosome partitioning 总被引:5,自引:0,他引:5
Judith W. Zyskind Amy L. Svitil W. Blaine Stine Matthew C. Biery Douglas W. Smith 《Molecular microbiology》1992,6(17):2525-2537
Escherichia coli cells deficient in RecA protein frequently contain an abnormal number of chromosomes after completion of ongoing rounds of DNA replication. This suggests that RecA protein may be required for correct timing of initiation of DNA replication; however, we show here that initiation of DNA replication is properly timed in recA mutants. We also find that more than 10% of recA mutant cells contain no DNA. These anucleate cells appear to arise from partitioning of all the DNA into one daughter cell and no DNA into the other daughter cell. Based on these and previously published results, we propose that RecA protein is required for equal partitioning of chromosomes into the two daughter cells. 相似文献
292.
293.
We often perform movements and actions on the basis of internal motivations and without any explicit instructions or cues. One common example of such behaviors is our ability to initiate movements solely on the basis of an internally generated sense of the passage of time. In order to isolate the neuronal signals responsible for such timed behaviors, we devised a task that requires nonhuman primates to move their eyes consistently at regular time intervals in the absence of any external stimulus events and without an immediate expectation of reward. Despite the lack of sensory information, we found that animals were remarkably precise and consistent in timed behaviors, with standard deviations on the order of 100 ms. To examine the potential neural basis of this precision, we recorded from single neurons in the lateral intraparietal area (LIP), which has been implicated in the planning and execution of eye movements. In contrast to previous studies that observed a build-up of activity associated with the passage of time, we found that LIP activity decreased at a constant rate between timed movements. Moreover, the magnitude of activity was predictive of the timing of the impending movement. Interestingly, this relationship depended on eye movement direction: activity was negatively correlated with timing when the upcoming saccade was toward the neuron''s response field and positively correlated when the upcoming saccade was directed away from the response field. This suggests that LIP activity encodes timed movements in a push-pull manner by signaling for both saccade initiation towards one target and prolonged fixation for the other target. Thus timed movements in this task appear to reflect the competition between local populations of task relevant neurons rather than a global timing signal. 相似文献
294.
Many rumors convey information about potential danger, even when these dangers are very unlikely. In four studies, we examine whether micro-processes of cultural transmission explain the spread of threat-related information. Three studies using transmission chain protocols suggest a) that there is indeed a preference for the deliberate transmission of threat-related information over other material, b) that it is not caused by a general negativity or emotionality bias, and c) that it is not eliminated when threats are presented as very unlikely. A forced-choice study on similar material shows the same preference when participants have to select information to acquire rather than transmit. So the cultural success of threat-related material may be explained by transmission biases, rooted in evolved threat-detection and error-management systems, that affect both supply and demand of information. 相似文献
295.
Douglas M. Bradley Francesca D. Beaman D. Blaine Moore Marieta Barrow Heaton 《Developmental neurobiology》1997,32(7):684-694
The study described below was performed as a continuation of a previous study in which we found reduced motoneuron number in lumbar spinal cord of the chick embryo following chronic ethanol administration from embryonic day 4 (E4) to E11. We sought to determine whether this reduction was due to primary ethanol toxicity or to enhancement of naturally occurring cell death (NOCD) and to determine whether administration of ethanol at a later period of development could also reduce motoneuron number. Earlier studies have shown that curare suspends NOCD in the chick embryo. By administering both ethanol and curare to these embryos from E4 to E11 and examining the lumbar spinal cord on E12, we determined that ethanol was directly toxic to motoneurons and reduced motoneuron number in the absence of NOCD. By administering ethanol from E10 to E15 and examining the lumbar spinal cord on E16, we determined that ethanol can reduce motoneuron number without altering spinal cord length during more than one stage of chick embryo development, and that ethanol toxicity is not dependent on NOCD. In addition, we demonstrated that ethanol does not affect the neurotrophic content of chick muscle when it is administered from E10 to E15. © 1997 John Wiley & Sons, Inc. J Neurobiol 32 : 684–694, 1997 相似文献
296.
Blaine J. Cole 《Evolution; international journal of organic evolution》2020,74(3):655-659
Most of the theory for the evolution of caste specialization in social insects assumes that increased efficiency in worker labor leads to specialization and increased worker efficiency gives colonies with behavioral specialists an advantage. However, there are an increasing number of studies that show that the task specialists within social insect colonies do not have the highest efficiency. Indeed, some studies show that some groups of workers are uniformly better than all other groups at every task. In this note, I adapt the principle of comparative advantage from economics to show that, rather than maximizing the payoff, specialization is advantageous when minimizing opportunity costs. This leads to the prediction that caste specialization should be associated with reduced opportunity costs rather than increased task efficiency. 相似文献
297.
Blaine J. Cole 《Journal of Insect Behavior》1991,4(2):129-137
Single, isolated worker ants are known to become spontaneously active and to respond to interactions with other, active ants. Here I explore the consequences of an interaction between two worker ants on the timing of activity. Isolated worker ants become active after an interval that is characteristic for each individual. The effect of an interaction between two worker ants is strongly dependent on when the interaction takes place. The effect of an interaction is always to decrease the expected interval until the onset of activity. By studying the effect of an interaction on subsequent intervals of activity, it is possible to reject the hypothesis that the change in timing of activity is due to a change in the characteristic period of activity. Rather, the data are consistent with the hypothesis that an interaction causes a phase shift in the normal activity oscillation. The phase-response curve is derived from the observational data. A knowledge of the dynamics of the interactions of individual ants is necessary in order to begin to reconstruct the patterns of colony behavioral activity. 相似文献
298.
A common signature of marine invasions worldwide is a significant loss of parasites (= parasite escape) in non-native host populations, which may confer a release from some of the harmful effects of parasitism (e.g., castration, energy extraction, immune activation, behavioral manipulation) and possibly enhance the success of non-indigenous species. In eastern North America, the notorious invader Carcinus maenas (European green crab) has escaped more than two-thirds its native parasite load. However, one of its parasites, a trematode (Microphallus similis), can be highly prevalent in the non-native region; yet little is known about its potential impacts. We employed a series of laboratory experiments to determine whether and how M. similis infection intensity influences C. maenas, focusing on physiological assays of body mass index, energy storage, and immune activation, as well as behavioral analyses of foraging, shelter utilization, and conspicuousness. We found little evidence for enduring physiological or behavioral impacts four weeks after experimental infection, with the exception of mussel handling time which positively correlated with cyst intensity. However, we did find evidence for a short-term effect of M. similis infection during early stages of infection (soon after cercarial penetration) via a significant drop in circulating immune cells, and a significant increase in the crabs’ righting response time. Considering M. similis is the only common parasite infecting C. maenas in eastern North America, our results for minimal lasting effects of the trematode on the crab’s physiology and behavior may help explain the crab’s continued prominence as a strong predator and competitor in the region. 相似文献
299.
Mohammad S Khorasani Sindi Diko Allison W Hsia Matthew J Anderson Damian C Genetos Dominik R Haudenschild Blaine A Christiansen 《Arthritis research & therapy》2015,17(1)
IntroductionPrevious studies in animal models of osteoarthritis suggest that alendronate (ALN) has antiresorptive and chondroprotective effects, and can reduce osteophyte formation. However, these studies used non-physiologic injury methods, and did not investigate early time points during which bone is rapidly remodeled prior to cartilage degeneration. The current study utilized a non-invasive model of knee injury in mice to investigate the effect of ALN treatment on subchondral bone changes, articular cartilage degeneration, and osteophyte formation following injury.MethodsNon-invasive knee injury via tibial compression overload or sham injury was performed on a total of 90 mice. Mice were treated with twice weekly subcutaneous injections of low-dose ALN (40 μg/kg/dose), high-dose ALN (1,000 μg/kg/dose), or vehicle, starting immediately after injury until sacrifice at 7, 14 or 56 days. Trabecular bone of the femoral epiphysis, subchondral cortical bone, and osteophyte volume were quantified using micro-computed tomography (μCT). Whole-joint histology was performed at all time points to analyze articular cartilage and joint degeneration. Blood was collected at sacrifice, and serum was analyzed for biomarkers of bone formation and resorption.ResultsμCT analysis revealed significant loss of trabecular bone from the femoral epiphysis 7 and 14 days post-injury, which was effectively prevented by high-dose ALN treatment. High-dose ALN treatment was also able to reduce subchondral bone thickening 56 days post-injury, and was able to partially preserve articular cartilage 14 days post-injury. However, ALN treatment was not able to reduce osteophyte formation at 56 days post-injury, nor was it able to prevent articular cartilage and joint degeneration at this time point. Analysis of serum biomarkers revealed an increase in bone resorption at 7 and 14 days post-injury, with no change in bone formation at any time points.ConclusionsHigh-dose ALN treatment was able to prevent early trabecular bone loss and cartilage degeneration following non-invasive knee injury, but was not able to mitigate long-term joint degeneration. These data contribute to understanding the effect of bisphosphonates on the development of osteoarthritis, and may support the use of anti-resorptive drugs to prevent joint degeneration following injury, although further investigation is warranted. 相似文献
300.
Boghigian BA Myint M Wu J Pfeifer BA 《Journal of industrial microbiology & biotechnology》2011,38(11):1809-1820
Natural products have long served as rich sources of drugs possessing a wide range of pharmacological activities. The discovery
and development of natural product drug candidates is often hampered by the inability to efficiently scale and produce a molecule
of interest, due to inherent qualities of the native producer. Heterologous biosynthesis in an engineering and process-friendly
host emerged as an option to produce complex natural products. Escherichia coli has previously been utilized to produce complex precursors to two popular natural product drugs, erythromycin and paclitaxel.
These two molecules represent two of the largest classes of natural products, polyketides and isoprenoids, respectively. In
this study, we have developed a platform E. coli strain capable of simultaneous production of both product precursors at titers greater than 15 mg l−1. The utilization of a two-phase batch bioreactor allowed for very strong in situ separation (having a partitioning coefficient
of greater than 5,000), which would facilitate downstream purification processes. The system developed here could also be
used in metagenomic studies to screen environmental DNA for natural product discovery and preliminary production experiments. 相似文献