A mutant of the motor protein kinesin that moves in both directions on microtubules

Molecular motors move directionally to either the plus or the minus end of microtubules or actin filaments. Kinesin moves towards microtubule plus ends, whereas the kinesin-related Ncd motor moves to the minus ends. The 'neck'--the region between the stalk and motor domain--is required for Ncd to move to microtubule minus ends, but the mechanism underlying directional motor movement is not understood. Here we show that a single amino-acid change in the Ncd neck causes the motor to reverse directions and move with wild-type velocities towards the plus or minus end; thus, the neck is functional but directionality is defective. Mutation of a motor-core residue that touches the neck residue in crystal structures also results in movement in both directions, indicating that directed movement to the minus end requires interactions of the neck and motor core. Low-density laser-trap assays show that a conformational change or working stroke of the Ncd motor is directional and biased towards the minus end, whereas that of the neck mutant occurs in either direction. We conclude that the directional bias of the working stroke is dependent on neck/motor core interactions. Absence of these interactions removes directional constraints and permits movement in either direction.     

A plus-end-directed motor enzyme that moves antiparallel microtubules in vitro localizes to the interzone of mitotic spindles.

Mitosis comprises a complex set of overlapping motile events, many of which involve microtubule-dependent motor enzymes. Here we describe a new member of the kinesin superfamily. The protein was originally identified as a spindle antigen by the CHO1 monoclonal antibody and shown to be required for mitotic progression. We have cloned the gene that encodes this antigen and found that its sequence contains a domain with strong sequence similarity to the motor domain of kinesin-like proteins. The product of this gene, expressed in bacteria, can cross-bridge antiparallel microtubules in vitro, and in the presence of Mg-ATP, microtubules slide over one another in a fashion reminiscent of microtubule movements during spindle elongation.     

Coalignment of vimentin intermediate filaments with microtubules depends on kinesin.

Intermediate filaments in most types of cultured cells coalign with microtubules. Depolymerization of microtubules results in collapse of vimentin and desmin intermediate filaments to the nucleus where they form a perinuclear cap. Collapse can also be induced by microinjection of antibodies against intermediate filament or microtubule proteins. Thus, two filament systems interact with each other. But the molecules mediating this interaction are unknown. One of the candidates for this role is a microtubule motor kinesin. Recent data showed that kinesin is involved in the plus end-directed movement of the membranous organelles along microtubules such as radial extension of lysosomes in macrophages and centrifugal movement of pigment in melanophores. Here we report that injection of the anti-kinesin antibody into human fibroblasts results in the redistribution of intermediate filaments to a tight perinuclear aggregate but had no effect on the distribution of microtubules. Thus, kinesin is involved not only in organelle movement but also in interaction of the two major cytoskeletal systems, intermediate filaments and microtubules.     

The Dam1 kinetochore ring complex moves processively on depolymerizing microtubule ends

Chromosomes interact through their kinetochores with microtubule plus ends and they are segregated to the spindle poles as the kinetochore microtubules shorten during anaphase A of mitosis. The molecular natures and identities of coupling proteins that allow microtubule depolymerization to pull chromosomes to poles during anaphase have long remained elusive. In budding yeast, the ten-protein Dam1 complex is a critical microtubule-binding component of the kinetochore that oligomerizes into a 50-nm ring around a microtubule in vitro. Here we show, with the use of a real-time, two-colour fluorescence microscopy assay, that the ring complex moves processively for several micrometres at the ends of depolymerizing microtubules without detaching from the lattice. Electron microscopic analysis of 'end-on views' revealed a 16-fold symmetry of the kinetochore rings. This out-of-register arrangement with respect to the 13-fold microtubule symmetry is consistent with a sliding mechanism based on an electrostatically coupled ring-microtubule interface. The Dam1 ring complex is a molecular device that can translate the force generated by microtubule depolymerization into movement along the lattice to facilitate chromosome segregation.     

同时包裹氟尿嘧啶和齐墩果酸的壳聚糖微球的研究

目的:制备同时包裹5-氟尿嘧啶及齐墩果酸丁二酸单酯的壳聚糖微球.方法:以微球回收率为指标,采用离子交联法制备同时包裹5-氟尿嘧啶及齐墩果酸丁二酸单酯的壳聚糖微球,通过单因素实验和正交实验,优化微球的制备工艺,考察了粒径分布和zeta电位等微球表面的理化性质,采用透析法考察其体外释放特性及其影响因素.结果:通过单因素考察和正交实验优化,氟尿嘧啶壳聚糖微球的包封率为53.9%,氟尿嘧啶和齐墩果酸丁二酸单酯与壳聚糖的质量比分别为1∶10和1∶30,微球形态圆整,表面光滑,粒径分布均匀,平均粒径为(563±101)nm,体外释放研究表明该微球具有一定的缓释效果.结论:采用离子交联法制备同时包裹5-氟尿嘧啶及齐墩果酸丁二酸单酯的壳聚糖微球工艺稳定可行,所得壳聚糖微球具有一定的缓释效果.     

混凝土自收缩的测定及若干因素对自收缩影响规律的研究

采用非接触式电涡流位移传感器设计了自密实混凝土自收缩试验方法,进行自密实混凝土自收缩试验,考察粉煤灰单掺、粉煤灰与矿渣复掺、胶结料用量、水胶比对自密实混凝土自收缩的影响规律,并在试验的基础上提出自密实混凝土的自收缩计算模型.研究表明,该模型能够准确地对自密实混凝土的自收缩进行有效预测,可供相关研究人员进行参考.     

二氧化硫污染治理现状及其研究进展

文中综述了脱硫的各种技术方法，对其中有代表性的烟气脱硫技术举例，并指出了当今脱硫技术方法选择及研究热点和方向，提出了对当今烟气脱硫技术选择的看法。     

城市河道整治工程建设资金筹措及运作思考

通过对城市河道整治工程建设内容功能与费用的分析，指出了传统模式下建设资金组成厦其存在的问题．对市场运作模式下建设资金筹措及运作进行了探讨。     

地磁场对彩色显像管的影响及减小方法

根据世界地磁图,计算了单个运动电子的全球受力分布,得出地磁场对彩色显像管具有不可忽视的影响;为减小地磁的影响,提出了一种有效的屏蔽措施,其屏蔽机理是利用铁磁材料的高磁导率对地磁场进行磁分路．此外,就屏蔽效果与现有的屏蔽方式作了对比分析．结果表明,采用该措施,地磁场影响明显减小．     

计算机中上溢数据的精确表示

文章讨论了上溢的数用数组和链表表示的方法和计算过程,所使用的大数超出常规数据类型,并给出具体表示和计算.     

Fe-ZSM-5分子筛上NO和N2O吸附行为及NO助N2O催化分解机理的研究

利用原位漫反射红外光谱法考察了NO 和N2O在液相离子交换法制备的Fe-ZSM-5分子筛上的吸附行为,并对NO助N2O催化分解的机理进行了研究.结果表明,NO和N2O均可吸附在Fe-ZSM-5分子筛表面的Brnsted 酸性位和价键补偿铁离子位上;且在高温下,NO和N2O均主要以价键补偿Fe离子的形式吸附在分子筛上.NO和O2在Fe-ZSM-5表面可反应生成N2O4、NO2和NO-3或NO-2;NO与N2O分解释放的O反应生成NO2,因而能起到加速N2O分解和提高Fe-ZSM-5分子筛催化活性的作用.     

珠江三角洲地区地方病主要类型及研究述评

珠江三角洲地区地方病主要有地氟病、地甲病和肝癌、鼻咽癌。地甲病和地氟病的主要病因可能分别是氟、碘元素。对与氟、碘元素产生颉颃作用、协同作用的元素的研究是进一步厘定地氟病、地甲病与地球化学环境关系的重要方面。作为流行病的肝癌和鼻咽癌的病因尚未探明，需要在前人研究的基础上，开展环境地球化学、医学地质学和多元统计分析等多学科方法的综合研究。     

基于理论与工程实践相结合的测试技术教学模式研究

针对测试技术课程教学中存在的缺点,分析了研究性教学和卓越计划的主旨,提出并详细介绍了基于理论与工程实践相结合教育模式的具体方法,从而实现知识积累和实践能力培养并重的教学核心理念。实践证明,该教学模式能够避免"重实践轻理论"的教学模式缺点,能够帮助学生克服畏难情绪,增强学生的创新能力。     

德拜温度不为常数时晶体的热力学函数

确定了晶体的德拜温度随温度变化的普适关系,导出了在此关系下晶体热力学函数的表达式.在此基础上,研究了铟的德拜温度和定压热容量随温度变化的规律.结果表明:理论计算与实验值基本一致.其中,在低温段和高温段理论值与实验值符合得较好,而中间段符合得稍差.     

浅析中国传统数学衰落的内在因素

通过分析中国古代社会、政治、经济、文化等特征,对比中西数学的异同,认为曾一度辉煌的中国传统数学衰落的一个重要原因在于其本身存在严重的缺陷,制约了中国传统数学的发展.     

HTML5对数字图书馆的影响

HTML5目前得到了苹果及谷歌公司这两大移动互联网巨头的大力支持而在智能手机和平板电脑上得到了广泛应用。同时,移动设备也已经成为图书馆服务的新载体。本文介绍了HTML5的主要特点,分析了HTML5在移动设备上的优势,讨论了其对数字图书馆发展的影响。【     

运动对肝细胞凋亡的影响及干预探讨

不同的运动方式和强度对肝细胞凋亡产生不同影响。本文从耐力训练、低氧训练和急性力竭、大强度训练等方面探讨运动状态下的肝细胞凋亡,从自由基理论、Bax、Bc l-2基因表达和Ca2+浓度等研究热点探讨肝细胞凋亡的机制。目前常采用抗氧化制剂对运动致肝细胞凋亡进行干预,通过清除体内的氧化过氧化产物,达到减少肝细胞非正常凋亡的目的。     

复合型高职专业设置的实践与思考

社会需要复合型人才,复合型高职专业设置,只有加强对专业设置的目标定位、系统设计、配置资源和质量控制等问题的研究与实践, 才能不断丰富专业内涵,形成专业特色,提升专业建设质量,顺应社会发展要求,为社会提供合格的高职复合型人才。     

基于减弱信息量滞后影响的RED算法

大量的测量表明,实际的网络业务普遍存在着在统计意义上的不可聚集性.在这种业务特性下,网络研究中的业务建模和性能分析都产生了许多新的问题.RED算法是一种十分重要的队列管理算法.目前国内研究RED算法的成果中,考虑到通信量滞后性的很少.本文主要研究了一种能减弱滞后性的负