The activity of ribosome modulation factor during growth of <Emphasis Type="Italic">Escherichia coli</Emphasis> under acidic conditions

Expression of the gene encoding ribosome modulation factor (RMF), as measured using an rmf-lacZ gene fusion, increased with decreasing pH in exponential phase cultures of Escherichia coli. Expression was inversely proportional to the growth rate and independent of the acidifying agent used and it was concluded that expression of rmf was growth rate controlled in exponential phase under acid conditions. Increased rmf expression during exponential phase was not accompanied by the formation of ribosome dimers as occurs during stationary phase. Nor did it appear to have a significant effect on cell survival under acid stress since the vulnerability of an RMF-deficient mutant strain was similar to that of the parent strain. Ribosome degradation was increased in the mutant strain compared to the parent strain at pH 3.75. Also, the peptide elongation rate was reduced in the mutant strain but not the parent during growth under acid conditions. It is speculated that the function of RMF during stress-induced reduction in growth rate is two-fold: firstly to prevent reduced elongation efficiency by inactivating surplus ribosomes and thus limiting competition for available protein synthesis factors, and secondly to protect inactivated ribosomes from degradation.     

青藏高原三种优势植物生物量分配的变化规律

该研究利用4个由高到低不同海拔的同质园实验,以青藏高原高寒草地优势植物垂穗披碱草(Elymus nutans)、矮嵩草(Kobresia humilis)和珠芽蓼(Polygonum viviparum)为对象,分析了植物个体根、茎、叶生物量分配及根冠比的变化规律及影响因素。结果表明:(1)植物个体根、茎、叶质量比和根冠比具有显著的种间差异;与垂穗披碱草和珠芽蓼相比,矮嵩草具有显著较高的根质量比而叶、茎质量比较低,所以其根冠比较高。(2)在向低海拔移栽的过程中,珠芽蓼叶质量比保持不变,茎质量比显著降低而根质量比显著升高,根冠比表现出显著上升的趋势;垂穗披碱草则相反,即叶、茎质量比显著升高而根质量比显著降低,根冠比表现出显著下降的趋势;矮嵩草根、茎、叶质量比和根冠比则无显著变化。(3)随着海拔降低,年均气温明显升高而年均降雨量明显降低,且在植物个体种源地和土壤基质保持一致的条件下,向低海拔移栽过程中温度是导致珠芽蓼根、茎、叶生物量分配及根冠比变化的重要因素,而水分是垂穗披碱草根、茎、叶生物量分配及根冠比变化的重要驱动因素;矮嵩草根、茎、叶生物量分配及根冠比受其遗传因素影响较大。因此,在将来暖干化的背景下,青藏高原高寒草地植物生物量的分配将会发生改变,导致它们对资源(光照、水分和土壤养分)获取和利用的变化而改变它们的种间关系,从而影响群落的物种多样性与组成,最终可能导致生态系统功能的变化。     

Solution structure of the E. coli ribosome hibernation promoting factor HPF: Implications for the relationship between structure and function

The 70S Escherichia coli ribosome dimerizes to form an inactive 100S ribosome during stationary phase, which is called “ribosome hibernation”. The hibernation promoting factor HPF plays a crucial role in 100S ribosome formation. However, YfiA, a known paralog of HPF inhibits 100S formation, although it shares high sequence similarity. Here, we report the first solution structure of HPF as determined by multi-dimensional NMR. HPF adopts βαβββα-fold and the overall structure is similar to YfiA as expected. However, detailed structure comparison based on the determined structure in this study revealed that there are remarkable differences around the C-terminal portion of helix α2, which is not predicted by homology modeling. Furthermore, some acidic residues conserved only in HPF are located at the rim of the common basic patch.     

rmf基因启动子识别因子选择性研究

分别用σ^(70)或σ^(38)因子和核心酶(Core enzyme)重建RNA聚合酶全酶(Holoenzyme)对含有rmf基因启动子的DNA模板进行体外转录。不同的限制性内切酶酶切片段模板证实了rmf基因转录起始位点,尽管rmf基因在大肠杆菌进入稳定期大量表达,但是其启动子对稳定期起重要作用的σ^(38)因子的识别能力很低,而只能被σ^(70)所识别。rmf基因启动子体外转录的最适温度为37℃,最适NaCl浓度为50mmol/L。     

Removal of both Ycf48 and Psb27 in Synechocystis sp. PCC 6803 disrupts Photosystem II assembly and alters QA oxidation in the mature complex

The Photosystem II (PS II) assembly factors Psb27 and Ycf48 are transiently associated with PS II during its biogenesis and repair pathways. We investigated the function of these proteins by constructing knockout mutants in Synechocystis sp. PCC 6803. In ΔYcf48 cells, PS II electron transfer and stable oxygen evolution were perturbed. Additionally, Psb27 was required for photoautotrophic growth of cells lacking Ycf48 and assembly beyond the RC47 assembly complex in ΔYcf48:ΔPsb27 cells was impeded. Our results suggest the RC47 complex formed in ΔYcf48 cells is defective and that this deficiency is exacerbated if CP43 binds in the absence of Psb27.     

稀有鮈鲫鳍细胞系的建立及其作为测定重金属毒性模型的探讨

稀有鮈鲫(Gobiocypris rarus)是我国特有的小型鲤科鱼类,自然分布于四川省彭州市、都江堰市、汉源县、石棉县、双流县等地,从1990年开始,中国科学院水生生物研究所对其分布区域、生物学、遗传纯化、饲养管理方法和繁殖技术等方面进行了大量的研究工作,是我国近十几年开始使用的一种优良的实验鱼.