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81.
Mitra P Zhang Y Rameh LE Ivshina MP McCollum D Nunnari JJ Hendricks GM Kerr ML Field SJ Cantley LC Ross AH 《The Journal of cell biology》2004,166(2):205-211
The mammalian tumor suppressor, phosphatase and tensin homologue deleted on chromosome 10 (PTEN), inhibits cell growth and survival by dephosphorylating phosphatidylinositol-(3,4,5)-trisphosphate (PI[3,4,5]P3). We have found a homologue of PTEN in the fission yeast, Schizosaccharomyces pombe (ptn1). This was an unexpected finding because yeast (S. pombe and Saccharomyces cerevisiae) lack the class I phosphoinositide 3-kinases that generate PI(3,4,5)P3 in higher eukaryotes. Indeed, PI(3,4,5)P3 has not been detected in yeast. Surprisingly, upon deletion of ptn1 in S. pombe, PI(3,4,5)P3 became detectable at levels comparable to those in mammalian cells, indicating that a pathway exists for synthesis of this lipid and that the S. pombe ptn1, like mammalian PTEN, suppresses PI(3,4,5)P3 levels. By examining various mutants, we show that synthesis of PI(3,4,5)P3 in S. pombe requires the class III phosphoinositide 3-kinase, vps34p, and the phosphatidylinositol-4-phosphate 5-kinase, its3p, but does not require the phosphatidylinositol-3-phosphate 5-kinase, fab1p. These studies suggest that a pathway for PI(3,4,5)P3 synthesis downstream of a class III phosphoinositide 3-kinase evolved before the appearance of class I phosphoinositide 3-kinases. 相似文献
82.
Couture JF Legrand P Cantin L Labrie F Luu-The V Breton R 《Journal of molecular biology》2004,339(1):89-102
The aldo-keto reductase rabbit 20alpha-hydroxysteroid dehydrogenase (rb20alpha-HSD; AKR1C5) is less selective than other HSDs, since it exerts its activity both on androgens (C19 steroids) and progestins (C21 steroids). In order to identify the molecular determinants responsible for this reduced selectivity, binary (NADPH) and ternary (NADP(+)/testosterone) complex structures were solved to 1.32A and 2.08A resolution, respectively. Inspection of the cofactor-binding cavity led to the identification of a new interaction between side-chains of residues His222 and Lys270, which cover the central phosphate chain of the cofactor, reminiscent of the "safety-belt" found in other aldo-keto reductases. Testosterone is stabilized by a phenol/benzene tunnel composed of side-chains of numerous residues, among which Phe54, which forces the steroid to take up an orientation markedly contrasting with that found in HSD ternary complexes reported. Combining structural, site-directed mutagenesis, kinetic and fluorescence titration studies, we found that the selectivity of rb20alpha-HSD is mediated by (i) the relaxation of loop B (residues 223-230), partly controlled by the nature of residue 230, (ii) the nature of the residue found at position 54, and (iii) the residues found in the C-terminal tail of the protein especially the side-chain of the amino acid 306. 相似文献
83.
84.
Development of Transformation System of Rice Based on Binary Bacterial Artificial Chromosome (BIBAC) Vector 总被引:1,自引:0,他引:1
Rui-Feng HE 《Acta Genetica Sinica》2006,33(3):269-276
85.
Edward N. Trifonov Idan Gabdank Danny Barash Yehoshua Sobolevsky 《Origins of life and evolution of the biosphere》2006,36(5-6):559-565
Evolution of the triplet code is reconstructed on the basis of consensus temporal order of appearance of amino acids. Several
important predictions are confirmed by computational sequence analyses. The earliest amino acids, alanine and glycine, have
been encoded by GCC and GGC codons, as today. They were succeeded, respectively, by A- and G-series of amino acids, encoded by pyrimidine-central and purine-central codons. The length of the earliest proteins is estimated
to be 6–7 residues. The earliest mRNAs were short G+C-rich molecules. These short sequences could have formed hairpins. This
is confirmed by analysis of modern prokaryotic mRNA sequences. Predominant size of detected ancient hairpins also corresponds
to 6–7 amino acids, as above. Vestiges of last common ancestor can be found in extant proteins in form of entirely conserved
short sequences of size six to nine residues present in all or almost all sequenced prokaryotic proteomes (omnipresent motifs).
The functions of the topmost conserved octamers are not involved in the basic elementary syntheses. This suggests an initial
abiotic supply of amino acids, bases and sugars.
Presented at: National Workshop on Astrobiology: Search for Life in the Solar System, Capri, Italy, 26 to 28 October, 2005. 相似文献
86.
线粒体形态学改变与细胞凋亡 总被引:4,自引:0,他引:4
近年来,对于线粒体形态学以及其在凋亡过程中的改变和作用的研究打破了传统的观点。正常情况下,线粒体在细胞内相互连接成管网状结构,并发生着频繁的融合与分裂。融合和分裂由一系列蛋白质介导,二者之间的动态平衡维持着线粒体的形态和功能。在细胞凋亡的早期,线粒体融合和分裂失平衡,导致线粒体管网状结构碎裂和嵴的重构,这些改变对线粒体随后的变化以及凋亡的发生具有重要的意义。融合和分裂的蛋白质不仅调控线粒体形态和细胞凋亡过程,也和某些凋亡相关疾病有关。此外,促凋亡的Bcl-2蛋白可能通过改变线粒体的构形来调控凋亡过程。 相似文献
87.
Boral S Gupta AN Bohidar HB 《International journal of biological macromolecules》2006,39(4-5):240-249
Controlled osmotic swelling and de-swelling measurements have been performed on gelatin, a polyampholyte, hydrogels suspended in water-ethanol marginal solvent at room temperature (20 degrees C) where the alcohol concentration was changed from 0 to 100% (v/v). The change in gel mass was monitored as function of time until osmotic equilibrium was established with the surrounding solvent. It was observed that osmotic pressure of polymer-solvent mixing, pi(m)相似文献
88.
Body fragmentation, in some animal groups, is a mechanism for survival and asexual reproduction. Lumbriculus variegatus (Müller, 1774), an aquatic oligochaete worm, is capable of regenerating into complete individuals from small body fragments
following injury and reproduces primarily by asexual reproduction. Few studies have determined the cellular mechanisms that
underlie fragmentation, either regenerative or asexual. We utilized boric acid treatment, which blocks regeneration of segments
in amputated fragments and blocks architomic fission during asexual reproduction, to investigate mechanistic relationships
and differences between these two modes of development. Neural morphallaxis, involving changes in sensory fields and giant
fiber conduction, was detected in amputated fragments in the absence of segmental regeneration. Furthermore, neural morphallactic
changes occurred as a result of developmental mechanisms of asexual reproduction, even when architomy was prevented. These
results show that fragmentation in L. variegatus, during injury or asexual reproduction, employs developmental and morphallactic processes that can be mechanistically dissociated
by boric acid exposure. In regeneration following injury, compensatory morphallaxis occurred in response to fragmentation.
In contrast, anticipatory morphallaxis was induced in preparation for fragmentation during asexual reproduction. Thus, various
forms of regeneration in this lumbriculid worm can be activated independently and in different developmental contexts. 相似文献
89.
In medical studies, paired binary responses are often observed for each study subject over timepoints or clusters. A primary interest is to investigate how the bivariate association and marginal univariate risks are affected by repeated measurements on each subject. To achieve this we propose a very general class of semiparametric bivariate binary models. The subject-specific effects involved in the bivariate log odds ratio and the univariate logit components are assumed to follow a nonparametric Dirichlet process (DP). We propose a hybrid method to draw model-based inferences. In the framework of the proposed hybrid method, estimation of parameters is done by implementing the Monte Carlo expectation-maximization algorithm. The proposed methodology is illustrated through a study on the effectiveness of tibolone for reducing menopausal problems experienced by Indian women. A simulation study is also conducted to evaluate the efficiency of the new methodology. 相似文献
90.
Haninec AL Voskas D Needles A Brown AS Foster FS Dumont DJ 《Biochemical and biophysical research communications》2006,345(4):1299-1307
To investigate the possible role of the Angiopoietins in vessel remodelling, we overexpressed one of the angiopoietins, Angiopoietin-1 (Ang1), in the hepatocytes of mice by means of the conditional binary transgenic system. Animals were examined by Doppler ultrasound, and dissected livers were analyzed by immunohistochemical staining. Double transgenic mice presented with enlarged spleens and kidneys, enlarged, disorganized blood vessels located near the surface of the liver, sprouting, dilation, and disorganization of liver lymphatics, and turbulent flow in about 1/4 of the blood vessels sampled. Most of these characteristics completely resolved within 12 weeks of turning off the expression of the Ang1 transgene, illustrating a dependence on the continual presence of Ang1 for maintenance of the vascular phenotype. Conditional Angiopoietin-1 overexpression in the liver of mice leads to a phenotype highly reminiscent of portal hypertension illustrating that Ang1 can drive both vascular and lymphatic vessel remodelling and may play a role in portal hypertension. 相似文献