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Metlitskaya A Kazakov T Kommer A Pavlova O Praetorius-Ibba M Ibba M Krasheninnikov I Kolb V Khmel I Severinov K 《The Journal of biological chemistry》2006,281(26):18033-18042
Microcin C is a ribosome-synthesized heptapeptide that contains a modified adenosine monophosphate covalently attached to the C-terminal aspartate. Microcin C is a potent inhibitor of bacterial cell growth. Based on the in vivo kinetics of inhibition of macromolecular synthesis, Microcin C targets translation, through a mechanism that remained undefined. Here, we show that Microcin C is a subject of specific degradation inside the sensitive cell. The product of degradation, a modified aspartyl-adenylate containing an N-acylphosphoramidate linkage, strongly inhibits translation by blocking the function of aspartyl-tRNA synthetase. 相似文献
2.
Spatial and daily variation in photosynthetic water-use efficiency was examined in leaves of Betula pendula Roth with respect to distribution of hydraulic conductance within the crown, morphological properties of stomata, and water
availability. Intrinsic water-use efficiency (A
n/g
s) was determined from gas-exchange measurements performed both in situ in a natural forest stand and on detached shoots under
laboratory conditions. In intact foliage, sun leaves demonstrated significantly higher (P < 0.001) A
n/g
s than shade leaves, as photosynthesis in the lower canopy was chronically limited by low light availability. However, this
difference reversed in the mid-day period under sufficient irradiance (I > 800 μmol m−2 s−1): A
n/g
s averaged 28.8 and 24.0 μmol mol−1 (P < 0.01) for shade and sun leaves, respectively. This last finding coincided with the data obtained in laboratory conditions:
under equivalent leaf water supply and light, A
n/g
s in shade foliage was greater (P < 0.001) than in sun foliage across a wide range of irradiance. Thus, shade foliage of B. pendula is characterized by inherently higher A
n/g
s than sun foliage, associated with more conservative stomatal behavior, and lower soil-to-leaf (K
T) and leaf hydraulic conductances. Under unlimited light conditions, a within-crown trade-off between A
n/g
s and K
T becomes apparent. Differences in stomatal conductance between the detached shoots from sunlit and shaded canopy layers were
largely attributable to the variation in stomatal morphology; significant relationships were established with characteristics
combining stomatal size and density (relative stomatal surface, stomatal pore area index). Stomatal morphology is very likely
involved in long-term adjustment of photosynthetic WUE. 相似文献
3.
We investigated phloem-xylem interactions in relation to leaf hydraulic capacity in hybrid aspen (Populus tremula L. × P. tremuloides Michx.) by using phloem girdling method. Removal of bark tissues (phloem girdling) at the branch base resulted in a substantial decline in stomatal conductance (gS), net photosynthetic rate (PN), and leaf hydraulic efficiency, and in increase of leaf water potential (ΨL). Although gS declined more than PN (83 versus 78 %), the ratio of intercellular to ambient CO2 concentrations (ci/ca) increased from 0.67 to 0.87 in three days after girdling. Girdling induced a decrease in leaf hydraulic conductance (KL) on average by 43 % (P = 0.006). The changes in gS and leaf conductance to water vapour were co-ordinated with KL only in girdled branches whereas intrinsic water-use efficiency was invariant to KL. The declines in KL with girdling were not accompanied by changes in potassium ion concentration ([K+]), electrical conductivity, or pH of xylem sap. The results suggest that phloem girdling at the branch base does not influence the recirculation of ions between the phloem and xylem in hybrid aspen and the decrease of KL in response to the manipulation is not related to changes in [K+] and total ionic content of xylem sap. 相似文献
4.
Svetlov MS Kommer A Kolb VA Spirin AS 《Protein science : a publication of the Protein Society》2006,15(2):242-247
Molecular chaperones of the Hsp70 family (bacterial DnaK, DnaJ, and GrpE) were shown to be strictly required for refolding of firefly luciferase from a denatured state and thus for effective restoration of its activity. At the same time the luciferase was found to be synthesized in an Escherichia coli cell-free translation system in a highly active state in the extract with no chaperone activity. The addition of the chaperones to the extract during translation did not raise the activity of the enzyme. The abrupt arrest of translation by the addition of a translational inhibitor led to immediate cessation of the enzyme activity accumulation, indicating the cotranslational character of luciferase folding. The results presented suggest that the chaperones of the Hsp70 family are not required for effective cotranslational folding of firefly luciferase. 相似文献
5.
Arne Sellin Arvo Tullus Aigar Niglas Eele Õunapuu Annika Karusion Krista Lõhmus 《Ecological Research》2013,28(3):523-535
A study was performed on saplings of silver birch (Betula pendula Roth) growing at the free air humidity manipulation site, which was established to investigate the effect of increased air humidity on tree performance and canopy functioning. The aim of the experiment was to simulate the impact of the increasing atmospheric humidity on forest ecosystems predicted for northern Europe. Artificially elevated relative humidity (RH), which causes transpirational flux to decrease, diminished nutrient supply to the foliage; leaf nitrogen content, phosphorus content and P:N ratio decreased. The changes in leaf nutritional status brought about a considerable decline in both photosynthetic capacity (A max, V cmax, J max) and tree growth rate. The manipulation induced diverse changes in tree hydraulic architecture and other functional traits. Different segments of the soil-to-leaf water transport pathway responded differently: leaf hydraulic conductance (K L) decreased, while hydraulic conductance of root systems (K R) and leaf-specific conductivity of stem-wood increased in response to elevated RH. Humidification caused the Huber values of stems to increase, thus reflecting changes in allocation patterns; relatively more resources were allocated to vascular tissue and less to foliage. The elevated RH induced substantial changes in specific leaf area (increased), branch- (decreased) and stem-wood density (decreased). The observed responses suggest that the expected climate-change-induced increase in the growth rate of trees at northern latitudes (boreal areas) due to the earlier start of the growing season in spring or higher carbon assimilation rate could be smaller or null if temperature rise is accompanied by a rise in atmospheric absolute humidity. 相似文献
6.
A comparative study of the 30S ribosomal subunit in the complex with protein S1 and the subunit depleted of this protein has been carried out by the hot tritium bombardment method. Differences in exposure of some ribosomal proteins within the 30S subunit depleted of S1 and within the 30S–S1 complex were found. It was concluded that protein S1 binds in the region of the neck of the 30S ribosomal subunit inducing a conformational change of its structure. 相似文献
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