侵染香蕉的黄瓜花叶病毒株系的形态和生物学特征

对香蕉花叶病广东三个代表分离物的形态和生物学特征进行了较为全面的研究。在六种鉴别寄主上,斑驳类（ＭＭ）和断续条纹类（ＢＳ）分离物侵染较多的寄主种类诱导较为严重的症状,连续条纹类（ＣＳ）分离物侵染能力较弱。电镜观察表明：ＢＳ、ＣＳ和ＭＭ三个代表分离物的粒子呈球状、其粒子直径分别为２２．５、２４．３和２７ｎｍ,纯化的病毒粒子电泳相对迁移率分别为０．７２、０．５６和０．５１,在西葫芦上的增殖速度：不管在子叶或真叶,都是ＭＭ最快、ＢＳ次之、ＣＳ最慢。从西葫芦接种叶运转出接种叶的速度：ＭＭ和ＢＳ相似、ＣＳ明显较慢。在烟草上,三个分离物的运转速度和增殖速度以ＭＭ最快、ＢＳ次之、ＣＳ最慢;而且在烟草上随着接种后时间的延长,三个分离物除ＭＭ维持高浓度的时间较长外,ＢＳ和ＣＳ的都很短。在西葫芦和烟草上提纯产量,ＭＭ类最多、ＢＳ类次之、ＣＳ类最低。     

创伤后巨噬细胞对T细胞白介素2及白介素2受体α基因表达的直接接触抑制作用

以25μg/ml的丝裂霉素C处理巨噬细胞30min,可阻断巨噬细胞白介素1(IL-1)、白介素6(IL-6)、肿瘤坏死因子(TNF)及前列腺素E_2(PGE_2)的合成与分泌。创伤小鼠巨噬细胞经丝裂霉素C处理后,可明显抑制正常T细胞白介素2(IL-2)mRNA及IL-2受体(IL-2R)αmRNA水平,并增强Ts细胞的抑制活性。去除T细胞中Ts细胞可使巨噬细胞的抑制作用消失。表明创伤后巨噬细胞可通过直接的细胞接触方式抑制T细胞IL-2及IL-2 Rα的基因表达,且这一作用是通过增加Ts细胞活性而实现的。     

Functional properties of ficoll and their influence on anther culture responses of wheat

The effects of ficoll in liquid culture media have been contradictory in previous reports. The objective of this study was to determine the functional properties of ficoll in potato 4 (P4) liquid induction medium and their influence on anther culture responses of wheat. Ficoll addition significantly (p0.01) reduced callus production from the anthers of spring wheat cv. Pavon 76. The reduction was directly related to the concentration of ficoll added within the range of 50 to 200 g l^-1 medium. Although the addition of ficoll significantly (p0.01) increased the percentage of regenerable calli and the ratio of green vs. albino plants, the final yield of green plants per 100 anthers was significantly lower. Consistent results also were obtained with four other spring wheat genotypes (Chris, Butte 86, WA 6916, and Edwall). Ficoll concentration affected the density, viscosity, and osmolality of the liquid media. The higher medium density caused by ficoll addition increased the percentage of floating calli, as well as the percentage of regenerable calli and the ratio of green vs. albino plants. However, the increased medium viscosity by ficoll addition significantly (p0.01) reduced callus production. Ficoll addition also increased medium osmolality, which affected callus production by interacting with the sugar concentration of the induction media. Using response functions, the estimated maltose concentration for maximum callus production was 105 g l^-1 for the standard P4 media, compared with 68 g l^-1 for the ficoll-containing P4 media. These results clearly demonstrate that ficoll addition to the liquid P4 induction medium containing high sucrose concentration (90 g l^-1) is deleterious to the maximum production of green plants from wheat anther culture.     

Substrate binding to Src: A new perspective on tyrosine kinase substrate recognition from NMR and molecular dynamics

Most signal transduction pathways in humans are regulated by protein kinases through phosphorylation of their protein substrates. Typical eukaryotic protein kinases are of two major types: those that phosphorylate‐specific sequences containing tyrosine (~90 kinases) and those that phosphorylate either serine or threonine (~395 kinases). The highly conserved catalytic domain of protein kinases comprises a smaller N lobe and a larger C lobe separated by a cleft region lined by the activation loop. Prior studies find that protein tyrosine kinases recognize peptide substrates by binding the polypeptide chain along the C‐lobe on one side of the activation loop, while serine/threonine kinases bind their substrates in the cleft and on the side of the activation loop opposite to that of the tyrosine kinases. Substrate binding structural studies have been limited to four families of the tyrosine kinase group, and did not include Src tyrosine kinases. We examined peptide‐substrate binding to Src using paramagnetic‐relaxation‐enhancement NMR combined with molecular dynamics simulations. The results suggest Src tyrosine kinase can bind substrate positioning residues C‐terminal to the phosphoacceptor residue in an orientation similar to serine/threonine kinases, and unlike other tyrosine kinases. Mutagenesis corroborates this new perspective on tyrosine kinase substrate recognition. Rather than an evolutionary split between tyrosine and serine/threonine kinases, a change in substrate recognition may have occurred within the TK group of the human kinome. Protein tyrosine kinases have long been therapeutic targets, but many marketed drugs have deleterious off‐target effects. More accurate knowledge of substrate interactions of tyrosine kinases has the potential for improving drug selectivity.     

Tunable differential conductance of single wall C/BN nanotube heterostructure

The transport properties and differential conductance of the heterostructures constructed by (5,5) single wall carbon nanotube (SWCNT) and (5,5) single wall boron nitride nanotube (SWBNNT) are investigated using density functional theory in combination with non-equilibrium Green’s functions. We find that the transmission conductance of (5,5) BN/C nanotube heterostructure is not only continually depressed as the BNNT region increases but also the drop of the conductance is uniform in the energy window (?1.43 eV, 1 eV), which leads to linear I–V dependence for the systems when the bias is within this energy range. Moreover, the differential conductance linearly decreases when n?≤?3 but exponentially decreases when n?≥?3 for (5,5)(BN) _n /C heterostructure. Such tunable differential conductance of (5,5) BN/C nanotube heterostructure mainly derives from the blockage of the transport channels induced by the semiconductive BN segment.

Somatic Mutations in Exocrine Pancreatic Tumors: Association with Patient Survival

KRAS mutations are major factors involved in initiation and maintenance of pancreatic tumors. The impact of different mutations on patient survival has not been clearly defined. We screened tumors from 171 pancreatic cancer patients for mutations in KRAS and CDKN2A genes. Mutations in KRAS were detected in 134 tumors, with 131 in codon 12 and only 3 in codon 61. The GGT>GAT (G12D) was the most frequent mutation and was present in 60% (80/134). Deletions and mutations in CDKN2A were detected in 43 tumors. Analysis showed that KRAS mutations were associated with reduced patient survival in both malignant exocrine and ductal adenocarcinomas (PDAC). Patients with PDACs that had KRAS mutations showed a median survival of 17 months compared to 30 months for those without mutations (log-rank P = 0.07) with a multivariate hazard ratio (HR) of 2.19 (95%CI 1.09–4.42). The patients with G12D mutation showed a median survival of 16 months (log-rank-test P = 0.03) and an associated multivariate HR 2.42 (95%CI 1.14–2.67). Although, the association of survival in PDAC patients with CDKN2A aberrations in tumors was not statistically significant, the sub-group of patients with concomitant KRAS mutations and CDKN2A alterations in tumors were associated with a median survival of 13.5 months compared to 22 months without mutation (log-rank-test P = 0.02) and a corresponding HR of 3.07 (95%CI 1.33–7.10). Our results are indicative of an association between mutational status and survival in PDAC patients, which if confirmed in subsequent studies can have potential clinical application.     

Synthesis,cytotoxicity and topoisomerase II inhibitory activity of lomefloxacin derivatives

A novel series of amide derivatives of lomefloxacin were synthesized and evaluated for their topoisomerase I and II inhibitory activity as well as cytotoxicity against a panel of five human cancer cell lines. Of the compounds prepared compounds 9d and 9g exhibited strong inhibition against topoisomerase II at 100 μM. In addition, docking studies were performed to predict the inhibition mode.     

Changes in structure and dynamics of the Fv fragment of a catalytic antibody upon binding of inhibitor

Binding of the product inhibitor p-nitrophenol to the monoclonal esterolytic antibody NPN43C9 has been investigated by performing NMR spectroscopy of the heterodimeric variable-domain fragment (Fv) of the antibody in the presence and absence of inhibitor. Structural information from changes in chemical shift upon binding has been related to the changes in local dynamics in the active site of the catalytic antibody using NMR relaxation measurements. Significant changes in the chemical shifts of the backbone resonances upon binding extend beyond the immediate vicinity of the antigen binding site into the interface between the two associated polypeptides that form the Fv heterodimer, a possible indication that the binding of ligand causes a change in the relative orientations of the component light (V(L)) and heavy (V(H)) chain polypeptides. Significant differences in backbone dynamics were observed between the free Fv and the complex with p-nitrophenol. A number of resonances, including almost all of the third hypervariable loop of the light chain (L3), were greatly broadened in the free form of the protein. Other residues in the antigen-binding site showed less broadening of resonances, but still required exchange terms (R(ex)) in the model-free dynamics analysis, consistent with motion on a slow timescale in the active site region of the free Fv. Binding of p-nitrophenol caused these resonances to sharpen, but some R(ex) terms are still required in the analysis of the backbone dynamics. We conclude that the slow timescale motions in the antigen-binding site are very different in the bound and free forms of the Fv, presumably due to the damping of large-amplitude motions by the bound inhibitor.     

红三叶人工草地营养元素的生物循环

 本文研究了我国北亚热带高海拔地区红三叶人工草地11种营养元素的生物循环特征。结果表明:1.营养元素的存留量、归还量和吸收量均可分为5个水平;(1)高量级：氮、钾、钙;(2)中量级：磷、镁;(3)低量级：铁;(4)少量级：锰、锌、铜、硼;(5)微量级：钼。2．红三叶群落地上部的净生产量、自然归还量和元素的存留量均显著高于地下部。3．红三叶人工草地的元素输出量以氮、钾、钙较大。此外,对草用和种用红三叶群落营养元素生物循环特征的差异进行了比较。为维持本区红三叶人工草地营养元素的平衡,目前必须施用磷肥,施用量不能小于250kg·hm-2过磷酸钙。