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881.
Olga Shakhova Phil Cheng Pravin J. Mishra Daniel Zingg Simon M. Schaefer Julien Debbache Jessica H?usel Claudia Matter Theresa Guo Sean Davis Paul Meltzer Daniela Mihic-Probst Holger Moch Michael Wegner Glenn Merlino Mitchell P. Levesque Reinhard Dummer Raffaella Santoro Paolo Cinelli Lukas Sommer 《PLoS genetics》2015,11(1)
882.
Summary The trmD operon of Escherichia coli consists of the genes for the ribosomal protein (r-protein) S16, a 21 kDa protein (21K) of unknown function, the tRNA(m1G37)methyltransferase (TrmD), and r-protein L19, in this order. Previously we have shown that the steady-state amount of the two r-proteins exceeds that of the 21K and TrmD proteins 12- and 40-fold, respectively, and that this differential expression is solely explained by translational regulation. Here we have constructed translational gene fusions of the trmD operon and lacZ. The expression of a lacZ fusion containing the first 18 codons of the 21K protein gene is 15-fold higher than the expression of fusions containing 49 or 72 codons of the gene. This suggests that sequences between the 18th and the 49th codon may act as a negative element controlling the expression of the 21K protein gene. Evidence is presented which demonstrates that this regulation is achieved by reducing the efficiency of translation. 相似文献
883.
Edward P. Glenn Pamela L. Nagler Kiyomi Morino Kevin R. Hultine 《Plant and Soil》2013,371(1-2):655-672
Background and aims
We sought to understand the environmental constraints on an arid-zone riparian phreatophtye, saltcedar (Tamarix ramosissima and related species and hybrids), growing over a brackish aquifer along the Colorado River in the western U.S. Depth to groundwater, meteorological factors, salinity and soil hydraulic properties were compared at stress and non-stressed sites that differed in salinity of the aquifer, soil properties and water use characteristics, to identify the factors depressing water use at the stress site.Methods
Saltcedar leaf-level transpiration (EL), LAI, and stomatal conductance (GS) were measured over a growing season (June–September) with Granier and stem heat balance sensors and were compared to those for saltcedar at the non-stress site determined in a previous study. Transpiration on a ground-area basis (EG) was calculated as EL?×?LAI. Environmental factors were regressed against hourly and daily EL and GS at each site to determine the main factors controlling water use at each site.Results
At the stress site, mean EG over the summer was only 30 % of potential evapotranspiration (ETo). GS and EG peaked between 8 and 9 am then decreased over the daylight hours. Daytime GS was negatively correlated with vapor pressure deficit (VPD) (P?<?0.05). By contrast, EG at the non-stress site tracked the daily radiation curve, was positively correlated with VPD and was nearly equal to ETo on a daily basis. Depth to groundwater increased over the growing season at both sites and resulted in decreasing EG but could not explain the difference between sites. Both sites had high soil moisture levels throughout the vadose zone with high calculated unsaturated conductivity. However, salinity in the aquifer and vadose zone was three times higher at the stress site than at the non-stress site and could explain differences in plant EG and GS.Conclusions
Salts accumulated in the vadose zone at both sites so usable water was confined to the saturated capillary fringe above the aquifer. Existence of a saline aquifer imposes several types of constraints on phreatophyte EG, which need to be considered in models of plant water uptake. The heterogeneous nature of saltcedar EG over river terraces introduces potential errors into estimates of ET by wide-area methods. 相似文献884.
S I Goodman D A Gallegos C J Pullin B Halpern R J Truscott G Wise B Wilcken E D Ryan D T Whelen 《American journal of human genetics》1980,32(5):695-699
Two pregnancies at risk for glutaric acidemia were monitored. In one, in which the fetus was not affected, glutaric acid was not detected in the amniotic fluid at amniocentesis (15 weeks) and the glutaryl-CoA dehydrogenase activity of cultured amniotic cells was normal. In the other, a marked elevation of glutaric acid in the amniotic fluid, together with deficiency of glutaryl-CoA dehydrogenase in amniotic cells, prompted termination of the pregnancy, and studies on the abortus confirmed the diagnosis of glutaric acidemia. Glutaric acidemia, is, thus, another inborn error of metabolism which can be diagnosed in utero. 相似文献
885.
St. Croix Claudette M.; Harms Craig A.; McClaran Steven R.; Nickele Glenn A.; Pegelow David F.; Nelson William B.; Dempsey Jerome A. 《Journal of applied physiology》1998,85(4):1556-1563
Twenty-eighthealthy women (ages 27.2 ± 6.4 yr) with widely varying fitnesslevels [maximal O2consumption (O2 max),31-70 ml · kg1 · min1]first completed a progressive incremental treadmill test to O2 max (totalduration, 13.3 ± 1.4 min; 97 ± 37 s at maximal workload), rested for 20 min, and then completed a constant-load treadmill test at maximal workload (total duration, 143 ± 31 s). Atthe termination of the progressive test, 6 subjects had maintained arterial PO2(PaO2) near resting levels, whereas 22 subjects showed a >10 Torr decrease inPaO2 [78.0 ± 7.2 Torr, arterial O2 saturation(SaO2), 91.6 ± 2.4%], andalveolar-arterial O2 difference (A-aDO2,39.2 ± 7.4 Torr). During the subsequent constant-load test, allsubjects, regardless of their degree of exercise-induced arterialhypoxemia (EIAH) during the progressive test, showed a nearly identicaleffect of a narrowed A-aDO2(4.8 ± 3.8 Torr) and an increase inPaO2 (+5.9 ± 4.3 Torr) andSaO2 (+1.6 ± 1.7%) compared with atthe end point of the progressive test. Therefore, EIAH during maximalexercise was lessened, not enhanced, by prior exercise, consistent withthe hypothesis that EIAH is not caused by a mechanismwhich persists after the initial exercise period and is aggravated bysubsequent exercise, as might be expected of exercise-inducedstructural alterations at the alveolar-capillary interface. Rather,these findings in habitually active young women point to a functionallybased mechanism for EIAH that is present only during the exerciseperiod. 相似文献
886.
Abstract. Two general models have been proposed to explain the structure of the plant community: the community-unit model of Clements and the continuum model of Whittaker and Curtis, the latter based on Gleason's individualistic distribution of species. It is generally assumed that most ecologists now accept the continuum model. Empirical evidence suggests, however, that the continuum in its current form does not fully describe the observed patterns of vegetation along environmental gradients. In this paper, we introduce the hierarchical continuum as a general concept to represent dynamic community structure along regional spatial gradients. The hierarchical continuum is derived from a combination of the individualistic distribution of species, hierarchical assemblage structure, and the core-satellite species hypothesis. The hierarchical continuum concept predicts that the distribution of species across sites in a region will be polymodal, which reflects hierarchical structure, and that the distribution and abundance of species within and between sites will be spatially and temporally dynamic. Regional distribution of plant species in North American tallgrass prairie, southeastern flood-plain hardwood forests, northern upland hardwood forests, and boreal forests were either bimodal or polymodal as predicted by the hierarchical continuum concept. Species in tallgrass prairie were spatially and temporally dynamic with an average turnover of 8–9 species per 50 m2 yr1. In addition, the hierarchical continuum concept predicts the potential for fractal (self-similar) patterns of community structure, and provides a framework for testable hypotheses concerning species distributions along environmental gradients. 相似文献
887.
888.
889.
890.
Glenn C. Conroy 《American journal of physical anthropology》1982,57(1):7-12
A discriminant analysis was performed on 226 ceboid skulls using data on emissary foramina size and shape. The purposes of the study are to 1) measure the success with which these discriminating variables can distinguish among platyrrhine genera and 2) derive a set of classification functions which will permit the classification of new cases with unknown group membership (i.e., fossil skulls). This technique is able to correctly classify 80% of the 226 ceboid skulls. Support is given to the allocation of Chiropotes, Cacajao, and Pithecia into one morphologically unified subfamily, Pitheciinae. Alouatta, Ateles, and Lagothrix also share many similarities in emissary foramina size and shape and their inclusion into one subfamily, Atelinae, is probably warranted. The distinctiveness of Cebus in these same morphological features is apparent. Possibilities for extending this procedure to study fossil lineages in platyrrhines are discussed. 相似文献