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941.
N-acyl-L-homoserine lactone quorum sensing controls butanediol fermentation in Serratia plymuthica RVH1 and Serratia marcescens MG1 下载免费PDF全文
Butanediol fermentation in two Serratia species is shown to be affected by N-acyl-L-homoserine lactone-dependent quorum sensing. Knockout of quorum-sensing signal production caused a shift towards enhanced acid production, resulting in early growth arrest, which was reversible by the addition of synthetic signal molecules. 相似文献
942.
Lucia Carbone Pietro D’addabbo Maria Francesca Cardone Maria Grazia Teti Doriana Misceo Gery M. Vessere Pieter J. de Jong Mariano Rocchi 《Chromosoma》2009,118(2):269-277
Although the human genome sequence is generally considered “finished”, the latest assembly (NCBI Build 36.1) still presents
a number of gaps. Some of them are defined as “clone gaps” because they separate neighboring contigs. Evolutionary new centromeres
are centromeres that repositioned along the chromosome, without marker order variation, during evolution. We have found that
one human “clone gap” at 18q21.2 corresponds to an evolutionary new centromere in Old World Monkeys (OWM). The partially sequenced
gap revealed a satellite-like structure. DNA stretches of the same satellite were found in the macaque (flanking the chromosome
18 centromere) and in the marmoset (New World Monkey), which was used as an outgroup. These findings strongly suggested that
the repeat was present at the time of novel centromere seeding in OWM ancestor. We have provided, therefore, the first instance
of a specific sequence hypothesized to have played a role in triggering the emergence of an evolutionary new centromere.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
943.
944.
Myofilament length-dependent activation is a universal property of striated muscle, yet the molecular mechanisms that underlie this phenomenon are incompletely understood. Additionally, the rate by which sarcomere length (SL) is sensed and then transduced to form length-dependent activation is unknown. Here, using isolated guinea-pig myocardium, we employed a rapid solution-switch single myofibril technique that allows for the study of contractile action/relaxation dynamics in the virtual absence of diffusion delays. We compared contraction kinetics obtained at submaximal activation at steady-state SL with contractions observed after rapid SL ramps to that same SL just before activation. Neither the activation and relaxation kinetics nor the final submaximal force development differed significantly between the two contraction modes for SL ramps as fast as 5 ms. We conclude that the transduction of the length signal by the cardiac sarcomere to modulate thin filament activation levels occurs virtually instantaneously, possibly resulting from structural rearrangements of the contractile proteins. 相似文献
945.
In many cellular signaling pathways, key components form clusters at the cell membrane. Although much work has focused on the mechanisms behind such cluster formation, the implications for downstream signaling remain poorly understood. Here, motivated by recent experiments, we use particle-based simulation to study a covalent modification network in which the activating component is either clustered or randomly distributed on the membrane. We find that whereas clustering reduces the response of a single-modification network, it can enhance the response of a double-modification network. The reduction is a bulk effect: a cluster presents a smaller effective target to a substrate molecule in the bulk. The enhancement, on the other hand, is a local effect: a cluster promotes the rapid rebinding and second activation of singly activated substrate molecules. As such, the enhancement relies on frequent collisions on a short timescale, leading to an optimal ratio of diffusion to association that agrees with typical measured rates. We complement simulation with analytic results at both the mean-field and first-passage distribution levels. Our results emphasize the importance of spatially resolved models, showing that significant effects of spatial correlations persist even in spatially averaged quantities such as response curves. 相似文献
946.
? Premise of the study: Current environmental changes may affect the dynamics and viability of plant populations. This environmental sensitivity may differ between species of different ploidy level because polyploidization can influence life history traits. We compared the demography and climatic sensitivity of two closely related ferns: the tetraploid Polystichum aculeatum and one of its diploid parents, Polystichum setiferum. ? Methods: Matrix models were used to assess the effects of life history variation on population dynamics under varying winter conditions. We analyzed the contributions of all key aspects of the fern life cycle to population growth. Our study is the first to also include the gametophyte generation. ? Key results: Projected population growth rate (λ) was much higher for the tetraploid P. aculeatum (1.516) than for P. setiferum (1.071) under normal winter conditions. During a year with harsh winter conditions, population growth of P. aculeatum was strongly reduced. This finding contradicts our expectation that the winter-hardy fronds of this species would allow high survival of harsh winters. Differences in λ between species and between years with different winter conditions were mostly caused by variation in gametophyte-related recruitment rates, a finding that shows the importance of including gametophytes in fern demographic studies. ? Conclusions: Our results indicate that populations of closely related ferns can show large differences in population performance, mainly related to recruitment rates and frond phenology, and that these differences may depend greatly on climatic conditions. Our findings provide a first indication that (allo)polyploidization in ferns can have a significant effect on population dynamics. 相似文献
947.
Steenhuis P Froemming J Reinheckel T Storch S 《Biochimica et biophysica acta》2012,1822(10):1617-1628
CLN7 is a polytopic lysosomal membrane glycoprotein of unknown function and is deficient in variant late infantile neuronal ceroid lipofuscinosis. Here we show that full-length CLN7 is proteolytically cleaved twice, once proximal to the used N-glycosylation sites in lumenal loop L9 and once distal to these sites. Cleavage occurs by cysteine proteases in acidic compartments and disruption of lysosomal targeting of CLN7 results in inhibition of proteolytic cleavage. The apparent molecular masses of the CLN7 fragments suggest that both cleavage sites are located within lumenal loop L9. The known disease-causing mutations, p.T294K and p.P412L, localized in lumenal loops L7 and L9, respectively, did not interfere with correct lysosomal targeting of CLN7 but enhanced its proteolytic cleavage in lysosomes. Incubation of cells with selective cysteine protease inhibitors and expression of CLN7 in gene-targeted mouse embryonic fibroblasts revealed that cathepsin L is required for one of the two proteolytic cleavage events. Our findings suggest that CLN7 is inactivated by proteolytic cleavage and that enhanced CLN7 proteolysis caused by missense mutations in selected luminal loops is associated with disease. 相似文献
948.
949.
Chronic infection with Helicobacter pylori strains expressing the bacterial oncoprotein CagA confers an increased risk of gastric cancer. While much is known about the ancestry and molecular evolution of Western, East Asian, and Amerindian cagA sequences, relatively little is understood about a fourth group, known as "J-Western," which has been detected mainly in strains from Okinawa, Japan. We show here that J-Western cagA sequences have a more widespread global distribution than previously recognized, occur in strains with multiple different ancestral origins (based on multilocus sequence typing [MLST] analysis), and did not arise recently. As shown by comparisons of Western and J-Western forms of CagA, there are 45 fixed or nearly fixed amino acid differences, and J-Western forms contain a unique 4-amino-acid insertion. The mean nucleotide diversity of synonymous sites (π(s)) is slightly lower in the J-Western group than in the Western and East Asian groups (0.066, 0.086, and 0.083, respectively), which suggests that the three groups have comparable, but not equivalent, effective population sizes. The reduced π(s) of the J-Western group is attributable to ancestral recombination events within the 5' region of cagA. Population genetic analyses suggest that within the cagA region encoding EPIYA motifs, the East Asian group underwent a marked reduction in effective population size compared to the Western and J-Western groups, in association with positive selection. Finally, we show that J-Western cagA sequences are found mainly in strains producing m2 forms of the secreted VacA toxin and propose that these functionally interacting proteins coevolved to optimize the gastric colonization capacity of H. pylori. 相似文献
950.
Dineke Frentz Charles A. B. Boucher Matthias Assel Andrea De Luca Massimiliano Fabbiani Francesca Incardona Pieter Libin Nino Manca Viktor Müller Breanndán ó. Nualláin Roger Paredes Mattia Prosperi Eugenia Quiros-Roldan Lidia Ruiz Peter M. A. Sloot Carlo Torti Anne-Mieke Vandamme Kristel Van Laethem Maurizio Zazzi David A. M. C. van de Vijver 《PloS one》2010,5(7)