Cooperative tandem binding of met repressor of Escherichia coli

We present biochemical and genetic data to support the hypothesis that the Escherichia coli met repressor, MetJ, binds to synthetic and natural operator sequences in tandem arrays such that repression depends not only on the affinity of the DNA-protein interaction, but also on protein-protein contacts along the tandem array. This represents a novel form of regulatory switch. Furthermore, there seems to be homology between the organization of the met and trp operators.     

Amino-terminal fragments of Escherichia coli lac repressor bind to DNA.

The N-terminal fragments (residues 1-51 and 1-59) obtained by selective tryptic cleavage of native lac repressor retain the ability to bind DNA. These fragments (headpieces) are monomeric and form complexes which resemble those of tetrameric repressor with non-operator DNA. But, they do not show the high specificity of repressor for operator sequences. The DNA binding has been demonstrated by filter-binding assay as well as in solution using absorption, circular dichroism, and fluorescence measurements.     

NaCl晶体中电子型色心的电子结构研究

运用密度泛函离散变分（DV-Xα）方法研究了NaCl晶体中可能存在的色心,模拟计算得到含色心的NaCl晶体的电子结构．计算结果表明,F、F2心在禁带中引入了新的能级;分析了可能存在的光学跃迁,并用过渡态方法计算得到相应的跃迁能量为2．74eV和1．74eV．该计算结果与实验测得的吸收光谱的峰值位置吻合较好．而F^＋心不存在光学跃迁吸收,但使晶体的禁带宽度变窄．计算结果还解释了NaCl晶体吸收光谱的结构起因．     

不同掺杂二氧化钛的电子和晶体结构与光催化性能的关系

对未掺杂、氮掺杂、碘掺杂和铂掺杂的锐钛矿TiO_2进行了第一性原理计算。结果表明,三种掺杂TiO_2带隙中都产生新的能带。这些新出现的能带是掺杂TiO_2响应可见光的原因。而且铂掺杂TiO_2的带隙缩小,响应波长更宽。铂掺杂和碘TiO_2的能带位置明显下移,表明其具有更强的氧化性。偏态密度分析表明掺杂元素提供的轨道参与了价带和导带的构成。通过对晶体结构的分析和TiO_6八面体偶极矩的计算,发现I掺杂后晶体结构明显畸变,其次是铂掺杂,氮掺杂几乎无畸变。而这种畸变产生的偶极矩能促进载流子的迁移,提高光催化活性。计算结果很好地解释了未掺杂和掺杂TiO_2在可见光照射下的光催化活性差异。     

大肠杆菌NADP特异性谷氨酸脱氢酶基因的克隆及其在大肠杆菌中的高效表达与纯化

谷氨酸脱氢酶是生物体内最主要的氧化脱氨基酶类，为了进一步研究其功能，我们以大肠杆菌DH5α菌株基因组DNA为模板和相应的寡聚脱氧核苷酸为引物，进行PCR扩增大肠杆菌NADP特异性谷氨酸脱氢酶基因(NADP-specific glutamate dehydrogenase，gdhA gene)，将所得DNA片断连接到质粒pUC18上，转化大肠杆菌DH5α，进行蓝白筛选和酶切鉴定，经测序证明序列正确无误后将gdhA基因连接到表达载体pTrcHisC上，在大肠杆菌BL21(DE3)中表达，经SDS-PAGE和双波长扫描分析，确定大肠杆菌谷氨酸脱氢酶在大肠杆菌中表达时以包涵体的形式存在，未能检测到可溶性蛋白的表达，表达量可达菌体总蛋白的15％以上．     

大肠杆菌硫氧还蛋白thioredoxin基因的克隆及表达

以大肠杆菌XL1blue为模板，通过PCR技术扩增大肠杆菌硫氧还蛋白基因，并将目的基因分别连接到克隆载体pUC18和表达载体pTrcHisC上，构建重组质粒．重组质粒pTrcHisC-TRX在大肠杆菌中高效表达，最后利用固定化金属螫合亲和层析技术(IMAC)获得较纯的目的蛋白，为进一步研究硫氧还蛋白的功能及其应用提供了条件．     

FtsZ ring structure associated with division in Escherichia coli

Genes for cell division have been identified in Escherichia coli by the isolation of conditional lethal mutations that block cell division, but do not affect DNA replication or segregation. Of these genes, ftsZ is of great interest as it acts earliest in the division pathway, is essential, its level dictates the frequency of division, and it is thought to be the target of two cell-division inhibitors, SulA, produced in response to DNA damage, and MinCD, which prevents division at old sites. Here we have used immunoelectronmicroscopy to localize the FtsZ protein to the division site. The results suggest that FtsZ self-assembles into a ring structure at the future division site and may function as a cytoskeletal element. The formation of this ring may be the point at which division is regulated.     

Influence of microgravity on protein crystal structures

Structural determination and comparison of microgravity and ground grown protein crystals have been carried out in order to investigate the effect of microgravity on the structure of protein crystals. Following the structural studies on the hen egg-white lysozyme cystals grown in space and on the ground, the same kind of comparative studies was performed with acidic phospholipase A₂ crystals grown in different gravities. Based on the results obtained so far, a conclusion could be made that microgravity might not be strong enough to change the conformation of polypeptide chain of proteins, but it may improve the bound waters’ structure, and this might be an important factor for microgravity to improve the protein crystal quality. In addition, the difference in the improvement between the two kinds of protein crystals may imply that the degree of improvement of a protein crystal in microgravity may be related to the solvent content in the protein crystal.     

大肠杆菌乙酸耐受株的代谢流分布

通过在基本培养基中的连续培养，比较了大肠杆菌耐乙酸突变株JL3碳源基本代谢流量分布与出发株JM101的差异，发现随比生长速率的增大，两者进入磷酸戊糖途径的碳流增加，进入三碳羧环的碳流减少。在相同的比生长速率下，突变株JL3中分配于磷酸戊糖途径的碳流所占比例高于JM101，在比生长速率0．626h^-1时，JL3进入磷酸戊糖途径的 占摄入碳流的33．2％，而JM101只占9．0％。计算得到J3力JM101关于ATP的最大菌体得率为10．2g/mol和5．68g／mol，维持系数为64．5mmol/(g.h)和82．3mmol/(kg.h），表明JL3的能量代谢效率高于JM101。     

2种Keggin型多金属氧酸盐化合物的合成和晶体结构

利用常规合成方法合成了2个由2,2′-联咪唑修饰的Keggin型多金属氧酸盐有机-无机杂化化合物:[H3(biim)2](C4H8O2)2[PW12O40].11H2O(1)和[H3(biim)2](C4H8O2)3[PMo12O40].3H2O(2)(H2biim=2,2′-联咪唑),并通过单晶X射线衍射、元素分析、IR光谱和电化学分析等进行了表征.结构分析表明化合物1属于单斜晶系,C2/c空间群,化合物2属于正交晶系,Pbca空间群.分子间通过静电引力作用和氢键作用形成了三维超分子网状结构.