Tissue-Specific Loss of DARS2 Activates Stress Responses Independently of Respiratory Chain Deficiency in the Heart

1. Download : Download high-res image (320KB)
2. Download : Download full-size image

     

Fusicoccin Activates the Plasma Membrane H+-ATPase by a Mechanism Involving the C-Terminal Inhibitory Domain

Plasma membrane vesicles isolated from spinach leaves incubated with the fungal toxin fusicoccin showed a twofold increase in ATP hydrolytic activity and a threefold increase in H+ pumping compared to controls. This increase in H+-ATPase activity was largely completed within 4 min of incubation and was not due to de novo synthesis of H+-ATPase as demonstrated by immunoblotting. Incubation with fusicoccin also resulted in a decrease in the apparent Km for ATP of the H+-ATPase from 0.22 to 0.10 mM. The fusicoccin-mediated activation of H+-ATPase activity and the accompanying decrease in the Km for ATP are changes very similar to those observed upon trypsin activation of the H+-ATPase, where an autoinhibitory domain in the C-terminal region of the H+-ATPase is removed. Thus, trypsin treatment of plasma membrane vesicles from control leaves gave a twofold increase in ATP hydrolytic activity and a threefold increase in H+ pumping, as well as a decrease in the apparent Km for ATP of the H+-ATPase from 0.22 to 0.10 mM. Trypsin treatment of plasma membranes from fusicoccin-incubated leaves did not further enhance the H+-ATPase activity, however, and neither was the Km for ATP further decreased. That trypsin really removed a small segment from the fusicoccin-activated H+-ATPase was confirmed by immunoblotting, which showed the appearance of a 90-kD band in addition to the native 100-kD H+-ATPase band upon trypsin treatment. Taken together, our data suggest that in vivo activation of the H+-ATPase by fusicoccin proceeds by a mechanism involving a displacement of the C-terminal inhibitory domain.     

The Analysis of Arabidopsis Nicotianamine Synthase Mutants Reveals Functions for Nicotianamine in Seed Iron Loading and Iron Deficiency Responses

Nicotianamine chelates and transports micronutrient metal ions in plants. It has been speculated that nicotianamine is involved in seed loading with micronutrients. A tomato (Solanum lycopersicum) mutant (chloronerva) and a tobacco (Nicotiana tabacum) transgenic line have been utilized to analyze the effects of nicotianamine loss. These mutants showed early leaf chlorosis and had sterile flowers. Arabidopsis (Arabidopsis thaliana) has four NICOTIANAMINE SYNTHASE (NAS) genes. We constructed two quadruple nas mutants: one had full loss of NAS function, was sterile, and showed a chloronerva-like phenotype (nas4x-2); another mutant, with intermediate phenotype (nas4x-1), developed chlorotic leaves, which became severe upon transition from the vegetative to the reproductive phase and upon iron (Fe) deficiency. Residual nicotianamine levels were sufficient to sustain the life cycle. Therefore, the nas4x-1 mutant enabled us to study late nicotianamine functions. This mutant had no detectable nicotianamine in rosette leaves of the reproductive stage but low nicotianamine levels in vegetative rosette leaves and seeds. Fe accumulated in the rosette leaves, while less Fe was present in flowers and seeds. Leaves, roots, and flowers showed symptoms of Fe deficiency, whereas leaves also showed signs of sufficient Fe supply, as revealed by molecular-physiological analysis. The mutant was not able to fully mobilize Fe to sustain Fe supply of flowers and seeds in the normal way. Thus, nicotianamine is needed for correct supply of seeds with Fe. These results are fundamental for plant manipulation approaches to modify Fe homeostasis regulation through alterations of NAS genes.     

Arginine Citrullination at the C-Terminal Domain Controls RNA Polymerase II Transcription

1. Download high-res image (125KB)
2. Download full-size image

     

The Dimerization Function of MinC Resides in a Structurally Autonomous C-Terminal Domain

Limited proteolysis of the Escherichia coli cell division inhibitor MinC reveals that its dimerization function resides in a structurally autonomous C-terminal domain. We show that cytoplasmic MinC is poised near the monomer-dimer equilibrium and propose that it only becomes entirely dimeric once recruited to the membrane by MinD.     

拟南芥中缺铁反应性microRNAs的鉴定

microRNA是一种非编码蛋白质的小分子RNA,参与了植物生长发育及环境胁迫响应的调控,主要通过对靶基因的负调控去影响生物学过程.基于前人对拟南芥全基因组microRNAs及其靶基因的预测,我们找到了靶向15个缺铁响应基因的22个microRNAs(miR158a、miR164c、miR172a、miR1887、miR2111ab、miR3933、miR395ade、miR414、miR828、miR831、miR837-3P、miR837-5P、miR854abcd、miR857、miR861-5P、miR864-5P).对这些microRNAs的启动子进行分析,发现分别有17、10和4个microRNAs启动子中包含缺铁响应元件IDE1、生长素响应元件和乙烯响应元件.进一步通过Poly(T)adaptor RT-PCR方法对这22个microRNAs在缺铁条件下的表达变化做了检测,结果显示,除miR158a和miR837-5P外的20个microRNAs在缺铁条件下的表达变化都有显著差异,且具有时间依赖性.这20个microRNAs可作为缺铁响应的候选microRNAs.     

缺铁敏感度不同的大豆品种对缺铁的适应机制

与供铁处理相比,对缺铁敏感的大豆品种“哈８３”幼苗在缺铁胁迫条件下根际没有酸化现象,根系对Ｆｅ（Ⅲ）的还原能力也没有明显增强。但抗缺铁的大豆品种“８７０１”幼苗根际则严重酸化,根系对Ｆｅ（Ⅲ）的还原能力显著增强;加入能抑制根系Ｈ＋－ＡＴＰ酶活性、减弱根际酸化作用的Ｈ＋－ＡＴＰ酶抑制剂正钒酸钠会降低根系对Ｆｅ（Ⅲ）的还原能力;说明根际酸化与根系还原Ｆｅ（Ⅲ）能力相互联系,初步证实根细胞原生质膜Ｈ＋－ＡＴＰ酶和缺铁诱导的还原酶相互偶联的假说。     

The C-Terminal Domain of Sin1 Interacts with the SWI-SNF Complex in Yeast

In the yeast Saccharomyces cerevisiae, the SWI-SNF complex has been proposed to antagonize the repressive effects of chromatin by disrupting nucleosomes. The SIN genes were identified as suppressors of defects in the SWI-SNF complex, and the SIN1 gene encodes an HMG1-like protein that has been proposed to be a component of chromatin. Specific mutations (sin mutations) in both histone H3 and H4 genes produce the same phenotypic effects as do mutations in the SIN1 gene. In this study, we demonstrate that Sin1 and the H3 and H4 histones interact genetically and that the C terminus of Sin1 physically associates with components of the SWI-SNF complex. In addition, we demonstrate that this interaction is blocked in the full-length Sin1 protein by the N-terminal half of the protein. Based on these and additional results, we propose that Sin1 acts as a regulatable bridge between the SWI-SNF complex and the nucleosome.     

The C-Terminal Domain of the mGluR1 Metabotropic Glutamate Receptor Affects Sensitivity to Agonists

Abstract: The metabotropic glutamate receptor (mGluR) subtype 1 exists as at least three variants (−1a, −1b, and −1c) generated by alternative splicing at the C-terminal domain. Fluorometric Ca²⁺ measurements were used to compare the concentration dependency of agonist-induced rises in intracellular free Ca²⁺ concentration ([Ca²⁺]_i) in human embryonic HEK 293 cells transiently expressing rat mGluR1a, mGluR1b, or mGluR1c. The rank order of agonist potencies was quisqualate ≫ (2 S, 1' S, 2' S )-2-(carboxycyclopropyl)glycine (L-CCG-I) > (1 S, 3 R )-1-aminocyclopentane-1,3-dicarboxylic acid [(1 S, 3 R )-ACPD] and did not differ among the splice variants. However, agonists were consistently more potent at mGluR1a than at mGluR1c and mGluR1b. In the same system, we characterized the agonist pharmacology of two chimeric rat mGluR3/1 receptors where the first and/or the second intracellular loop(s) and the C-terminal domain were exchanged with the corresponding mGluR1a or mGluR1c sequences and that were previously shown to mediate elevations in [Ca²⁺]_i in response to agonists. The potency of agonists was higher at the chimera having the C-terminus of mGluR1a as compared with those having the mGluR1c C-terminus. Both chimeric mGluR3/1 receptors had the same rank order of agonist potencies: L-CCG-I ≫ (1 S, 3 R )-ACPD ∼ quisqualate. These data support the hypothesis that the C-terminal domain of mGluRs plays a role in determining the potency of agonists for inducing mGluR-mediated functional responses.