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141.
Structural comparison of the prokaryotic ribosomal proteins L7/L12 and L30   总被引:7,自引:0,他引:7  
The structures of two prokaryotic ribosomal proteins, the carboxyterminal half of L7/L12 from Escherichia coli (L12CTF) and L30 from Bacilus stearothermophilus display a remarkably similar fold in which alpha-helices pack onto one side of an antiparallel, three-stranded, beta-pleated sheet. A detailed comparison of the structures by least-squares methods reveals that more than two-thirds of the alpha carbons can be superimposed with a root mean square distance of 2.33 A. The principal difference is an extra alpha-helix in L12CTF. The sequences of the proteins display a distinct conservation in regions which are crucial to the common fold, in particular the hydrophobic core. It is proposed that the similarity is a result of divergent evolution.  相似文献   
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The photoacoustic gas uptake signal correlates with carbonicanhydrase activity in transgenic tobacco plants, various levelsof which were induced by antisense RNA [Price et al. (1994)Planta 193: 339]. This is taken as evidence that the uptakesignal is caused by C02-solubilisation upon light-driven stromaalkalisation rather than by (O2-uptake. (Received December 8, 1997; Accepted January 31, 1998)  相似文献   
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To determine the contribution of photosynthesis on stomatal conductance, we contrasted the stomatal red light response of wild-type tobacco (Nicotiana tabacum 'W38') with that of plants impaired in photosynthesis by antisense reductions in the content of either cytochrome b(6)f complex (anti-b/f plants) or Rubisco (anti-SSU plants). Both transgenic genotypes showed a lowered content of the antisense target proteins in guard cells as well as in the mesophyll. In the anti-b/f plants, CO(2) assimilation rates were proportional to leaf cytochrome b(6)f content, but there was little effect on stomatal conductance and the rate of stomatal opening. To compare the relationship between photosynthesis and stomatal conductance, wild-type plants and anti-SSU plants were grown at 30 and 300 micromol photon m(-2) s(-1) irradiance (low light and medium light [ML], respectively). Growth in ML increased CO(2) assimilation rates and stomatal conductance in both genotypes. Despite the significantly lower CO(2) assimilation rate in the anti-SSU plants, the differences in stomatal conductance between the genotypes were nonsignificant at either growth irradiance. Irrespective of plant genotype, stomatal density in the two leaf surfaces was 2-fold higher in ML-grown plants than in low-light-grown plants and conductance normalized to stomatal density was unaffected by growth irradiance. We conclude that the red light response of stomatal conductance is independent of the concurrent photosynthetic rate of the guard cells or of that of the underlying mesophyll. Furthermore, we suggest that the correlation of photosynthetic capacity and stomatal conductance observed under different light environments is caused by signals largely independent of photosynthesis.  相似文献   
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The availability of a complete genome database for the cyanobacterium Synechocystissp. PCC6803 (glucose-tolerant strain) has raised expectations that this organism would become a reference strain for work aimed at understanding the CO2-concentrating mechanism (CCM) in cyanobacteria. However, the amount of physiological data available has been relatively limited. In this report we provide data on the relative contributions of net HCO3 uptake and CO2 uptake under steady state photosynthetic conditions. Cells were compared after growth at high CO2 (2% v/v in air) or limiting CO2 conditions (20 ppm CO2). Synechocystishas a very high dependence on net HCO3 uptake at low to medium concentrations of inorganic carbon (Ci). At high Ci concentrations net CO2 uptake became more important but did not contribute more than 40% to the rate of photosynthetic O2 evolution. The data also confirm that high Ci cells of Synechocystissp. PCC6803 possess a strong capacity for net HCO3 uptake under steady state photosynthetic conditions. Time course experiments show that induction of maximal Ci uptake capacity on a shift from high CO2 to low CO2 conditions was near completion by four hours. By contrast, relaxation of the induced state on return of cells to high CO2, takes in excess of 230 h. Experiments were conducted to determine if Synechocystissp. PCC6803 is able to exhibit a `fast induction' response under severe Ci limitation and whether glucose was capable of causing a rapid inactivation in Ci uptake capacity. Clear evidence for either response was not found. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
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Cyanobacteria, algae, aquatic angiosperms and higher plants have all developed their own unique versions of photosynthetic CO2 concentrating mechanisms (CCMs) to aid Rubisco in efficient CO2 capture. An important aspect of all CCMs is the critical roles that the specialised location and function that various carbonic anhydrase enzymes play in the overall process, participating the interconversion of CO2 and HCO3 species both inside and outside the cell. This review examines what we currently understand about the nature of the carbonic anhydrase enzymes, their localisation and roles in the various CCMs that have been studied in detail. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
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