钒取代Keggin型杂多酸的多层组装和电催化性能研究

用层层组装的方法在 4 -氨基苯甲酸预修饰的玻碳电极上交替沉积过渡金属钒取代的杂多酸H3 PW6V6O6- 4 0 (简称 PW6V6)和联吡啶锇取代的聚乙烯吡啶 (QPVP-Os) .用表面等离子体共振 (SPR)技术和循环伏安 (CV)法对多层膜进行了表征 .结果表明 ,多层膜的生长均匀 ,平均厚度为 2 .88nm.还研究了多层膜对亚硝酸根 (NO- 2 )和溴酸根 (Br O- 3 )的催化还原活性.

The paleoclimatic events and cause in the Okinawa Trough during 50 kaBP

Planktonic foraminiferal delta O-18 record for core DGKS9603 from the Okinawa Trough shows a series of climatic fluctuations and sudden cooling events in short time scale during 50 kaBP, which appear to correlate closely to the Younger Dryas and Heinrich events H1-5 recorded in Chinese loess, the South China Sea, the North Atlantic cores and the Greenland ice cores. Three polarity reversal events, correlating to Gothenburg, Mungo and Laschamp events, approximately correspond to Heinrich events H1, H3 and H5 respectively, which could be a cause of global climate changes. The delta O-18 curve of the Okinawa Trough is well associated with the grain size record of the Lijiayuan loess profile in northwestern China and is somewhat different from the climate fluctuations documented in the Greenland ice cores. These correlation results indicate that regional factors play an important role in controlling the climate changes in the East Asia, and the East Asian Monsoon could be the prominent regional controlling factor.

Millennial-scale paleoceanography in Okinawa Trough during Late Quaternary period

Based on the analyses of foraminifer and accelerator mass spectrometer radiocarbon dating in DGKS9603 core from mid-Okinawa Trough close to bottom, oscillation curve, which expressed the relation between the surface water temperature and the depth, has been obtained by using foraminifer analysis and calculation of FP-12E transfer function. The whole core indicated seven cold phases and eight warm phases. Obvious expression of low temperature event during Middle and Late Holocene, YD,H1,H2,H3 and H4 events, as well as the short cold phase during the middle last glacial period, implied that short shifts since 50 kaBP would have been global significance. Sedimentation rate during cold phases is usually faster than that in warm stages, with the lowest rate in Holocene, which may be connected with rising sea level and principal axial of Kuroshio Current moving to west. Volcanic activities highly developed in Okinawa Trough during the Quaternary period, thus abundant volcanic glass and pumice were well preserved.

两种红树林植物黄槿和长梗肖槿化学成分研究

由于红树林植物的重要药用价值及其特殊的生长环境，越来越多的学者关注于红树林植物的活性成分及其作用机理的研究。本论文对两种药用红树林植物黄槿（Hibiscus tiliaceus L.）和长梗肖槿（Thespesia populneoides (Roxb.) Kostel）的化学成分进行了系统研究。对从其中分离得到的部分化合物进行了初步的抗菌活性筛选。 黄槿和长梗肖槿均采自海南岛，干燥粉碎的样品用90％的乙醇水以及1：1氯仿-甲醇混合溶液室温浸泡提取得总浸膏，将总浸膏悬浮于水中，分别用石油醚和乙酸乙酯萃取，获得石油醚相和乙酸乙酯相萃取物。 采用常规的硅胶柱层析、制备薄层层析、凝胶Sephadex LH-20柱层析、反相硅胶柱层析、以及重结晶等手段，从黄槿和长梗肖槿的乙酸乙酯相中共分离得到43个化合物。利用各种现代波谱技术（IR、UV、MS、HR-MS、1D-NMR、2D-NMR等）确定了38个化合物的结构。其中，从黄槿的乙酸乙酯相中分离得到22个化合物，鉴定了其中19个化合物的结构，包括3个新的三萜类化合物(H1*-H3*)以及15个首次从该种中报道的化合物。从长梗肖槿的乙酸乙酯相中分离得到21个化合物，鉴定了其中19个化合物的结构，这些化合物皆为首次从该种中报道，其中1个为新的倍半萜类化合物T1*。本文为首次报道长梗肖槿的化学成分。 对分离得到的部分样品进行了抗菌活性测试，仅T1*表现微弱的抗金黄色葡萄球菌活性，抑菌圈直径为8mm（阳性对照氯霉素的抑菌圈直径为20mm），其余各样品在测试浓度下对测试菌株均未表现出活性。

栉孔扇贝核心组蛋白的基因结构及H2A抗菌活性的研究

栉孔扇贝是我国传统的海水养殖品种，但自1997 年以来，养殖扇贝陆续爆发的大规模死亡，不但造成了巨大的经济损失，而且严重影响了该产业的健康发展。目前，虽然针对扇贝养殖环境、病原以及养殖技术等方面开展了大量的研究工作，提出了许多防病治病的措施，并取得了一定的成效。但由于引起养殖扇贝病害的病原和发病原因的多样性，大量使用抗菌素和农药后造成病原微生物抗药性的提高以及对环境造成的严重破坏，贝类养殖业要摆脱病害的困扰，必须开辟新的疾病防治途径。 从扇贝自身的免疫防御因子入手，筛选和克隆参与免疫防御的功能基因，尤其是一些新颖的具有抗菌活性的分子，对于深入探讨扇贝的免疫防御机制，指导扇贝的遗传改良和抗病品系的培育具有重要的意义；另一方面，可对抗菌效应物实现重组表达，开发新型的病害预防治疗制剂，取代目前普遍使用的抗生素和化学药物。抗菌效应物是机体在免疫应答过程中产生的多肽类物质，对侵入生物体内的细菌、病毒具有很强的免疫杀灭作用，对抗菌效应物的研究有助于深入了解机体先天性免疫防御的机制。 本研究在同源克隆策略的基础上，从利用构建的Genome Walking 文库中克隆到了栉孔扇贝核心组蛋白群的全长序列，该串联重复序列全长5671bp，包括各一个拷贝的组蛋白H4, H2B, H2A 和 H3。所有的核心组蛋白在3’侧翼序列均具有与其在细胞周期进化模式相关的特征结构，即两个不同的终止信号：发卡结构和至少一个多聚腺苷酸信号序列（AATAAA）。在5’区域的起始密码子上游37–45 bp处的保守的CAP位点（5’-PyCATTCPu-3’）存在于除H2B外的每一个基因中；规则的TATA 和CAAT元件也在核心组蛋白群中的个别的基因中找到。在H2B 和H2A基因的启动子区域，对于定位转录起始位点非常重要的元件（5’-GATCC-3’）也相对保守； 在H2B启动子区域存在着与其特征序列（5’-GGAATAAACGTATTC-3’）相似性很高的序列结构5’-GGATCGAAACGTTC-3’。增强子序列只发现存在于H4 和 H3基因中，其序列结构与组蛋白增强子序列(5’-TGATATATG-3’)基本匹配。在组蛋白基因群中存在着一些保守的序列和重复结构表明组蛋白基因的进化是采取“生与死的进化模 式”并伴随着强的纯化选择压力，使得该基因群变异较少以保持其基本功能。同时，利用18S rRNA做参照，探讨了H2A 和H2B作为分子系统进化分析的潜在分子标记，表明组蛋白H2A 和H2B可以作为分子系统进化分析得候选分子，它们在区分近缘种的分辨率上表现出了更高的灵敏度。该研究结果为进一步定性软体动物组蛋白重复单位提供了基础。 在脊椎动物中，组蛋白H2A通过特异性剪切其N末端产生新颖的抗菌肽的形式来参与宿主的免疫应答反应，在软体动物中是否存在同样的机制还未有研究报道。本研究利用上述克隆的H2A基因研究了其在病原胁迫下的表达变化规律并对其N末端39aa进行了重组表达和抗菌活性分析，以期为开发和利用软体动物的新颖的抗菌肽提供理论依据。半定量RT-PCR发现血细胞中H2A 的mRNA 在微生物感染前后的表达量没有任何显著的变化，表明H2A本身并不直接参与对病原的清除过程或者说病原微生物并不能诱导H2A的表达。因此，我们推测该基因可能象脊椎动物一样以前体形式存在，经剪切后参与宿主的免疫应答过程，为此我们研究了H2A的N末端的抗菌活性。通过将与脊椎动物buforin I同源的H2A的N末端39aa克隆到毕赤酵母表达载体pPIC9K实现了该基因N末端的重组表达。抑菌实验表明，重组产物具有广谱的抗菌活性，其对供试的革兰氏阳性菌藤黄微球菌表现出显著的抗菌活性，而对革兰氏阴性菌（鳗弧菌、亮弧菌）的抑菌活性则相对较弱；此外，重组产物对毕赤酵母GS115也表现出一定的杀菌活性，证明其具有抗真菌活性。上述研究结果证明组蛋白H2A的N末端是一种潜在的抗菌肽，但该抗菌肽是否参与机体的免疫应答过程需要进一步的深入研究。

塔里木盆地塔中—巴楚地区早二叠世岩浆岩地球化学特征及其成因

Tazhong-Bachu region is located in the Western Tarim basin.The early Permian magmatic rocks occur in the earth surface of Tazhong-Bachu region are mainly distributed in Kepintag,Mazhartag and Wajilitag region. There are a lot of wells, in which researchers found the early Permian magmatic rocks,in desert cover area.Most magmatic rocks are basic rocks, a few of which are ultrabasic rocks and intermediate-acid magmatic rocks.The ultrabasic rocks are are mainly occur in the Cryptoexplosive Breccia Pipes ,which is located in the volcanic complex body of Wajilitag region.The basic rocks can be divided into three rock types：The first type of the magmatic rocks in Tazhong-Bachu region is volcanic rock ,which occurs in the Lower Permian Kupukuziman Formation and Kaipaizileike Formation. Most Volcanic rocks are basalts,a few of which are volcanic breccias and pyroclastic rocks.The basalts are distributed in stratiform occurrences and interbeded the clastic rocks in Kepintag region.The attitudes of the basalts are nearly horizontal.Columnar Joints, gas pore textures and amygdaloidal structure are to develop in basalts.The second type of the magmatic rocks in Tazhong-Bachu region is diabase,which occurs in Mazhartag region.Diabase dike swarms occur in the stratums of Silurian, Devonian, Carboniferous and Lower Permian.They make from NNW direction to SSE direction, the obliquity of stratum is greater than 60°, and the dike thickness is form several cm to several meters. Diabasic texture is found in the rocks .The first type of the magmatic rocks in Tazhong-Bachu region are gabbro- pyroxenite rocks ,which occur in the Wajilitag igneous complex body. The intermediate-acid magmatic rocks, which are mainly syenites, are located in Mazhartag and Wajiltag region. But they are small in the whole Tazhong-Bachu region.There are intermediate-acid magmatic rocks,which are mainly dacite,in the northeast part of the wells in Tazhong-Bachu region.But ,it is not found in earth surface.Through systematical geochemical research of early Permian magmatic rocks,which are distributed in Kepintag,Mazhartag, Wajilitag region and the wells such as F1 well、Z1 well、Z13 well、TZ18 well、H3 well、H4 well et al., the focus on the geochronologic characteristics, the main element,trace element and REE geochemistry, the mineralogic characteristics, the Sr-Nd and Pb isotopic characteristics are put forward. The main points are: 1、A combined study of CL imaging and LA-ICP-MS U-Pb dating were carried out for zircon grains of the magmatic rocks in the Tazhong-Bachu region from the Tarim basin.The results of the systematic zircon LA-ICP-MS U-Pb dating reveal 272±6Ma to 291±10Ma for the magamatic rocks. It indicated that Early Permian is an important period of magmatic acvivity in the Tazhong-Bachu region. 2、There are a big hunch in the curves of primitive mantle-normalized trace element concentrations in the early Permian magmatic rocks from Kepintag, Mazhartag, Wajilitag region and the 14 wells. Light rare earth elements are comparatively rich and heavy rare earth elements are comparatively poor. The slope rates are same between light rare erath elements and heavy rare earth elements. It is not like the curves of the basalts in the convergent margin of plate , in which the slope rates of light rare erath elements is bigger than the alope rates of heavy rare erath elements, and the curves of heavy rare earth elements are comparatively flat. The magmatic rocks of Tazhong-Bachu region rarely have the characteristics of the basalts in the convergent margin of plate, which is that Tantalum, Niobium and Titanium are much poor, and Zirconium, Hafnium and Phosphorus are moderately poor. The magamatic rocks are mostly alkaline, which is indicated by the dots of the (Na2O+K2O)-SiO2 identification diagram. All of these indicate that the early Permian magmatic rocks were formed in an extension environment of intraplate. 3、The Thorium abundance is high and Tantalum abundance is low in most magmatic rocks from Tazhong-Bachu reguion, which is formed for crustal contamination.In the Th/Yb-Ta/Yb identification diagram，most dots are in the region, which means active continental margin, but a few dots are in the region, which means mantle source. It indicated the feeding of continental crust materials. 4、The magnesium content of the olvines from Wagilitag region is richest, and the olvines from Kepintag region is poorest in the tree region. 5、Through the the Sr-Nd and Pb isotopic study of the basalts and diabases from the F1 well core, Z1 well core, Z13 well core,TZ18 well core, and the basalts，gabbros, diabases(diabase-prophyrites) and pl-peridotites from Kepintag,Mazhartag, Wajilitag region , it indicated that all isotopic data is similar and close to enriched mantle.

100块南极格罗夫山陨石的类型划分及其岩石学特征

根据岩石矿物学研究，包括岩石结构、橄榄石的Fa值和低钙辉石的Fs值以及金属模式含量等，100块格罗夫山陨石分别被划分为：4块H3型、11块H4型（其中一块为H4-an）、10块H5型、3块H6型、2块L3型、6块L4型、31块15型、32块L6型和1块LL4型。格罗夫山普通球粒陨石在类型分布上，其比例和南极以及非南极普通球粒陨石有显著不同，说明可能存在相当数量的成对陨石。分类陨石样品比较新鲜，其中98块陨石的风化程度为W1，仅有2块陨石风化程度分别为W2和W3。另外，这些陨石中冲击程度较高的样品占有一定比例，它们是研究冲击作用的理想样品。

稳定氮同位素在环境污染示踪中的应用进展

自然界的氮循环已被严重扰乱,失衡的氮循环过程中产生的一些氮氧化物和氮氢化物(如N2O、NO-3 、NO -2 、N H3 、NH +4 等) 是全球温室效应、水体富营养化和酸雨危害的主要贡献者。稳定氮同位素作为一种有效的示踪手段,在研究氮循环特别是污染氮源的识别方面有重要意义。本文在简要总结氮的同位素分馏效应的基础上,重点论述和分析了稳定氮同位素在植被O土壤O地下水系统和大气系统中的氮源识别,并结合研究现状探讨了研究前景。

巢湖沉积物δ^13C（org）和δ^15N记录的生态环境演化过程

通过对巢湖2处柱状沉积物样品中δ^13Corg、δ^15N、C/N比值、TOC和TN含量的测定,分析了近百年来巢湖沉积物有机质的来源,探讨受人类活动影响的湖泊生产力变化和富营养化过程.结果表明,巢湖沉积物有机质的主要来源是水生藻类,陆生有机质的输入量较少,但是城市污染物的输入与农业面源污染的影响是不可忽视的.巢湖沉积物剖面上,δ^13Corg、δ^15N、TOC和TN含量变化按沉积深度可以明显划分为2个阶段：①10 cm以下,H3点δ^13Corg波动在-21.74‰- -19.34‰的范围内,其余数据表现相对平缓,湖泊内的生物物种是固氮植物和非固氮植物共存,2个采样点具有不同的湖泊营养化进程;②10 cm至表层段,2个剖面的δ^13Corg迅速减小,δ^15N、TOC和TN则是显著增大,巢湖闸的建成使得内源营养物质快速积累,湖泊初始生产力水平迅速提高,富营养化加剧.

我国部分南极陨石的分类和宇宙成因核素10Be和26Al的研究

随着我国南极陨石的大量回收，对陨石的研究也越来越深入。本文主要对我国部分南极陨石和沙漠陨石开展了三方面的工作：（1）我国部分南极陨石的分类；（2）陨石中宇宙成因核素10Be和26Al的化学分离、纯化实验；（3）我国部分南极陨石和沙漠陨石的全岩化学组成分析和宇宙成因核素10Be和26Al的初步研究。 1、我国部分南极陨石的分类研究 通过对我国19次南极科考队回收的4448块陨石中24块南极普通球粒陨石的矿物、岩石分析，将这24块陨石化学－岩石类型进行了划分，分别为1个H3型（GRV 021603）、2个H4型（GRV 020200和GRV 021493）、4个H5型（GRV 020048、GRV 020078、GRV 020129和GRV 020236）、2个H6型（GRV 020075和GRV 020226）、1个L4型（GRV 021563）、8个L5型（GRV 020047、GRV 020283、GRV 020297、GRV 021547、GRV 021547、GRV 021581、GRV 021615和GRV 023771）、5个L6型（GRV 020103、GRV 020155、GRV 021505、GRV 021711和GRV 022171）、1个LL4型（GRV 020029）和1个LL6型（GRV 021496）。在此基础上，将我国的南极陨石和美国的南极陨石进行了类型和质量分布模型的对比。结果表明，我国南极陨石比美国南极陨石具有相对高的L群丰度；我国的南极陨石质量分布模型与美国南极陨石一致。 2、陨石中宇宙成因核素10Be和26Al的化学分离、纯化实验 在前人关于陨石中宇宙成因核素10Be和26Al的分离方法基础上，通过多次模拟样品的分离实验，成功地将陨石中Be和Al进行了分离、纯化。并且进一步改善了前人的分离方法，将Be的淋洗液由原来的120ml减少为90ml。在此基础上，用空白样品和吉林陨石的硅酸盐样品对整个化学分离实验进行了检验，并将所获得的BeO和Al2O3粉末用加速器质谱（AMS）进行了10Be和26Al的测试。根据所测定的10Be和26Al数据，计算得到吉林陨石的暴露年龄为0.52Ma，这一结果与前人所获得的吉林陨石第二阶段的暴露年龄0.4Ma接近。这一结果再次证明了陨石中宇宙成因核素10Be和26Al的分离流程是成功的，同时也说明本次所测的吉林陨石样品为吉林陨石第二阶段暴露辐射的样品。 3、我国部分南极陨石和沙漠陨石的全岩化学组成分析以及宇宙成因核素10Be和26Al的初步研究 对我国13块南极陨石和3块沙漠陨石进行了全岩化学成分的分析，其结果进一步证明了这些陨石由岩石、矿物分析所划分的类型的正确性。在这些陨石类型和全岩分析的基础上，对它们进行了宇宙成因核素10Be和26Al的初步分析。得到其中4块南极陨石和2块沙漠陨石的暴露年龄和居地年龄，这些陨石暴露年龄的范围为2.09－3.05Ma，居地年龄为0－0.23Ma。

地外物质中铂族等亲铁元素的分析及应用

长久以来，对于陨石金属相的全岩研究主要使用中子活化分析方法（INAA），该方法具有灵敏度高、无损样品及制样简单等优点，但它无法测定所有铂族元素（PGEs）。随着分析技术的发展，电感耦合等离子质谱（ICP-MS）越来越广泛地应用于地质学领域，但在地外物质的应用中研究较少。 本论文在分析方法上，首先在国内开展了球粒陨石金属相和铁陨石的主、微量元素的ICP-AES和ICP-MS实验分析方法研究，对四块球粒陨石的金属相以及四块铁陨石进行了分析，初步讨论了星云凝聚和小行星热变质中亲铁元素的变化特征，进一步揭示了星云的凝聚过程、以及铁陨石的结晶过程。对新发现的乌拉斯台铁陨石所做的研究表明，该陨石和新疆陨石可能为成对陨石。并将研究延伸到地外撞击事件的研究中，通过对浙江煤山P/T界线层的样品进行分析，对当时的生物大灭绝事件给出了合理解释。 乌拉斯台铁陨石是在我国新疆新发现的一块铁陨石，其发现地点距离新疆铁陨石（Armanty）约130公里。我们应用ICP-MS分析了乌拉斯台铁陨石（IIIE），以及新疆铁陨石（IIIE）、南丹铁陨石（IIICD）和Mundrabilla铁陨石（IIICD）的全岩组成，结果显示和参考文献有很好的一致性，证明了该分析方法的可行性。我们对乌拉斯台铁陨石进行了系统的岩石学、矿物学、以及微量元素分析，该陨石的岩石结构属于粗粒八面体，铁纹石带宽为1.2  0.2 mm。合纹石以各种微观结构大量存在于该陨石中。陨磷镍铁矿以富镍（30.5-55.5%）的形式出现在合纹石中，或者与陨硫铁，陨硫铬铁矿等共生。并通过计算获知该陨石的冷却速率约为20℃/Myr。其岩石矿物学特征和全岩组成和新疆铁陨石相似，二者都落在IIIE化学群的范围，因此，我们将乌拉斯台铁陨石划分为IIIE化学群，并初步认为和新疆铁陨石是成对陨石。同时，对吉林球粒陨石（H5）、安龙球粒陨石（H5）、以及南极陨石GRV 9919（L3）和GRV 021603（H3）四块球粒陨石金属相进行的研究显示，球粒陨石金属相的亲铁元素配分模式主要与元素的挥发性相关，具有难熔元素基本上平坦分布，而中等和强挥发性元素随其挥性的增高而趋于贫化的特征。 铂族元素的研究不仅在讨论星云凝聚过程中亲铁元素的分异、金属-硅酸盐分异与核-幔的形成，以及金属熔体的结晶分异方面有着重要的意义，对于讨论地外物质的示踪也有着重要的作用。铂族元素在地壳中高度亏损，但在大部分地外物质中富集，因此通常将Ir的异常已否作为是否有地外物质加入的重要依据之一。距今2.51亿年前的二叠纪-三叠纪（P/T界线）时期，发生了地质历史上最大规模的生物灭绝事件，然而对于该事件的诱因却一直存有争议，主要存在两种观点：“地外撞击”和“火山喷发”。我们使用锍镍火试金和同位素稀释法，结合Te共沉淀， 应用ICP-MS分析技术，对我国煤山二叠纪-三叠纪界线层的样品进行了Ir、Ru、Rh、Pt和Pd的测定。火试金方法结果显示Ir的含量为0.053 ng/g，而同位素稀释法对P/T界线事件层样品的分析结果显示，Ir的含量在0.005-0.028 ng/g，两种分析方法的结果均显示没有Ir的正异常。将PGE使用碳质球粒陨石标准化后，整个配分模式呈现出高度分异，Ir/Pd的比值为0.02-0.03CI，明显不同于各类陨石。相反，该界线层样品的PGE配分模式和西伯利亚玄武岩（甚至也可能和峨眉山玄武岩）相似，证明了该界线层样品中的PGE可能来源于玄武岩。P/T界线层样品中PGE的含量从富含黄铁矿的壳层24f向26层呈上升趋势，且在26层为最大值，然后在28层回落，这种趋势可能暗示了玄武岩最大规模的喷发可能出现在26层。该结果有力地证明了P/T界线时期的生物灭绝事件与火山喷发的相关性，给一直存有争议的二叠纪-三叠纪生物灭绝事件提供了新的证据。

HDAC6 and Ubp-M BUZ domains recognize specific C-terminal sequences of proteins.

The BUZ/Znf-UBP domain is a protein module found in the cytoplasmic deacetylase HDAC6, E3 ubiquitin ligase BRAP2/IMP, and a subfamily of ubiquitin-specific proteases. Although several BUZ domains have been shown to bind ubiquitin with high affinity by recognizing its C-terminal sequence (RLRGG-COOH), it is currently unknown whether the interaction is sequence-specific or whether the BUZ domains are capable of binding to proteins other than ubiquitin. In this work, the BUZ domains of HDAC6 and Ubp-M were subjected to screening against a one-bead-one-compound (OBOC) peptide library that exhibited random peptide sequences with free C-termini. Sequence analysis of the selected binding peptides as well as alanine scanning studies revealed that the BUZ domains require a C-terminal Gly-Gly motif for binding. At the more N-terminal positions, the two BUZ domains have distinct sequence specificities, allowing them to bind to different peptides and/or proteins. A database search of the human proteome on the basis of the BUZ domain specificities identified 11 and 24 potential partner proteins for Ubp-M and HDAC6 BUZ domains, respectively. Peptides corresponding to the C-terminal sequences of four of the predicted binding partners (FBXO11, histone H4, PTOV1, and FAT10) were synthesized and tested for binding to the BUZ domains by fluorescence polarization. All four peptides bound to the HDAC6 BUZ domain with low micromolar K(D) values and less tightly to the Ubp-M BUZ domain. Finally, in vitro pull-down assays showed that the Ubp-M BUZ domain was capable of binding to the histone H3-histone H4 tetramer protein complex. Our results suggest that BUZ domains are sequence-specific protein-binding modules, with each BUZ domain potentially binding to a different subset of proteins.

Histone modifications within the human X centromere region.

Human centromeres are multi-megabase regions of highly ordered arrays of alpha satellite DNA that are separated from chromosome arms by unordered alpha satellite monomers and other repetitive elements. Complexities in assembling such large repetitive regions have limited detailed studies of centromeric chromatin organization. However, a genomic map of the human X centromere has provided new opportunities to explore genomic architecture of a complex locus. We used ChIP to examine the distribution of modified histones within centromere regions of multiple X chromosomes. Methylation of H3 at lysine 4 coincided with DXZ1 higher order alpha satellite, the site of CENP-A localization. Heterochromatic histone modifications were distributed across the 400-500 kb pericentromeric regions. The large arrays of alpha satellite and gamma satellite DNA were enriched for both euchromatic and heterochromatic modifications, implying that some pericentromeric repeats have multiple chromatin characteristics. Partial truncation of the X centromere resulted in reduction in the size of the CENP-A/Cenp-A domain and increased heterochromatic modifications in the flanking pericentromere. Although the deletion removed approximately 1/3 of centromeric DNA, the ratio of CENP-A to alpha satellite array size was maintained in the same proportion, suggesting that a limited, but defined linear region of the centromeric DNA is necessary for kinetochore assembly. Our results indicate that the human X centromere contains multiple types of chromatin, is organized similarly to smaller eukaryotic centromeres, and responds to structural changes by expanding or contracting domains.

Salicylic acid biosynthesis is enhanced and contributes to increased biotrophic pathogen resistance in Arabidopsis hybrids.

Heterosis, the phenotypic superiority of a hybrid over its parents, has been demonstrated for many traits in Arabidopsis thaliana, but its effect on defence remains largely unexplored. Here, we show that hybrids between some A. thaliana accessions show increased resistance to the biotrophic bacterial pathogen Pseudomonas syringae pv. tomato (Pst) DC3000. Comparisons of transcriptomes between these hybrids and their parents after inoculation reveal that several key salicylic acid (SA) biosynthesis genes are significantly upregulated in hybrids. Moreover, SA levels are higher in hybrids than in either parent. Increased resistance to Pst DC3000 is significantly compromised in hybrids of pad4 mutants in which the SA biosynthesis pathway is blocked. Finally, increased histone H3 acetylation of key SA biosynthesis genes correlates with their upregulation in infected hybrids. Our data demonstrate that enhanced activation of SA biosynthesis in A. thaliana hybrids may contribute to their increased resistance to a biotrophic bacterial pathogen.

Electrostatic Energetics of Bacillus subtilis Ribonuclease P Protein Determined by Nuclear Magnetic Resonance-Based Histidine pKa Measurements.

The pKa values of ionizable groups in proteins report the free energy of site-specific proton binding and provide a direct means of studying pH-dependent stability. We measured histidine pKa values (H3, H22, and H105) in the unfolded (U), intermediate (I), and sulfate-bound folded (F) states of RNase P protein, using an efficient and accurate nuclear magnetic resonance-monitored titration approach that utilizes internal reference compounds and a parametric fitting method. The three histidines in the sulfate-bound folded protein have pKa values depressed by 0.21 ± 0.01, 0.49 ± 0.01, and 1.00 ± 0.01 units, respectively, relative to that of the model compound N-acetyl-l-histidine methylamide. In the unliganded and unfolded protein, the pKa values are depressed relative to that of the model compound by 0.73 ± 0.02, 0.45 ± 0.02, and 0.68 ± 0.02 units, respectively. Above pH 5.5, H22 displays a separate resonance, which we have assigned to I, whose apparent pKa value is depressed by 1.03 ± 0.25 units, which is ∼0.5 units more than in either U or F. The depressed pKa values we observe are consistent with repulsive interactions between protonated histidine side chains and the net positive charge of the protein. However, the pKa differences between F and U are small for all three histidines, and they have little ionic strength dependence in F. Taken together, these observations suggest that unfavorable electrostatics alone do not account for the fact that RNase P protein is intrinsically unfolded in the absence of ligand. Multiple factors encoded in the P protein sequence account for its IUP property, which may play an important role in its function.