DNA twisting and the effects of non-contacted bases on affinity of 434 operator for 434 repressor.

The bacteriophage 434 repressor regulates gene expression by binding with differing affinities to the six operator sites on the phage chromosome. The symmetrically arrayed outer eight base pairs (four in each half-site) of these 14-base-pair operators are highly conserved but the middle four bases are divergent. Although these four base pairs are not in contact with repressor, operators with A.T or T.A base pairs at these positions bind repressor more strongly than those bearing C.G or G.C, suggesting that these bases are important for the repressor's ability to discriminate between operators. There is evidence that the central base pairs influence operator function by constraining the twisting and/or bending of DNA. Here we show that there is a relationship between the intrinsic twist of an operator, as determined by the sequence of its central bases, and its affinity for repressor; an operator with a lower affinity is undertwisted relative to an operator with higher affinity. In complex with repressor, the twist of both high- and low-affinity operators is the same. These results indicate that the intrinsic twist of DNA and its twisting flexibility both affect the affinity of 434 operator for repressor.     

Ethylation interference and X-ray crystallography identify similar interactions between 434 repressor and operator

In the crystal structure of a repressor-operator complex (the 434 repressor DNA-binding domain and its 14-base pair (bp) operator), Anderson et al. elsewhere in this issue identify six positions of likely contact between repressor protein and phosphates of the DNA backbone. At each of these positions, electron densities of protein and DNA merge. Experiments presented here indicate that intact 434 repressor approaches these phosphates very closely when it is bound to DNA in solution. Specifically, when any one of these phosphates is ethylated, repressor cannot bind to the modified operator. We also identify another position where ethylation has a significant but less dramatic effect on repressor binding, and note that in the structure, repressor closely approaches this phosphate. Our results strongly support the idea that the interactions between protein and the DNA phosphate backbone in the crystallized complex are the same as those made by intact repressor to operator DNA in solution. In addition, our results suggest that DNA is slightly bent by repressor binding.     

Structure of a phage 434 Cro/DNA complex

Comparison of the crystal structure of a complex of the phage 434 Cro protein and a synthetic DNA operator with the complex of the same operator and the 434 repressor DNA-binding domain shows different DNA conformations in the two structures. Binding of the protein determines the precise conformation of the DNA in each case.     

Crystal structure of the lambda repressor and a model for pairwise cooperative operator binding

Bacteriophage lambda has for many years been a model system for understanding mechanisms of gene regulation. A 'genetic switch' enables the phage to transition from lysogenic growth to lytic development when triggered by specific environmental conditions. The key component of the switch is the cI repressor, which binds to two sets of three operator sites on the lambda chromosome that are separated by about 2,400 base pairs (bp). A hallmark of the lambda system is the pairwise cooperativity of repressor binding. In the absence of detailed structural information, it has been difficult to understand fully how repressor molecules establish the cooperativity complex. Here we present the X-ray crystal structure of the intact lambda cI repressor dimer bound to a DNA operator site. The structure of the repressor, determined by multiple isomorphous replacement methods, reveals an unusual overall architecture that allows it to adopt a conformation that appears to facilitate pairwise cooperative binding to adjacent operator sites.     

A new-specificity mutant of 434 repressor that defines an amino acid-base pair contact

The repressor encoded by bacteriophage 434 binds to its operators by inserting a 'recognition' alpha-helix into the major groove of the DNA. We have identified an amino acid-base pair contact that determines (in part) the DNA-binding specificity of 434 repressor. The identification is based on the properties of a 'new-specificity' mutant, named Repressor [Ala 28], which bears the substitution of Ala for Gln at the first residue of its recognition alpha-helix. Repressor [Ala 28] binds with high affinity to a particular doubly mutant operator bearing the same substitution at position 1 in each half-site, but does not bind to either the wild-type operator or to other mutant operators. We describe molecular models of residue 28-base pair 1 interactions that account for the binding specificities of both the mutant and wild-type proteins.     

非接触测量系统中标定矩阵的研究

摄像机标定矩阵是非接触测量系统中的重要研究内容.主要介绍一种新的摄像机标定矩阵修正方法.实验表明,该标定方法操作简便,标定快速、准确.     

Crystal structure of trp repressor/operator complex at atomic resolution

The crystal structure of the trp repressor/operator complex shows an extensive contact surface, including 24 direct and 6 solvent-mediated hydrogen bonds to the phosphate groups of the DNA. There are no direct hydrogen bonds or non-polar contacts to the bases that can explain the repressor's specificity for the operator sequence. Rather, the sequence seems to be recognized indirectly through its effects on the geometry of the phosphate backbone, which in turn permits the formation of a stable interface. Water-mediated polar contacts to the bases also appear to contribute part of the specificity.     

Riemann-Roch算子与Dirac算子的一个注记

给出了算子Э^-＋Э^-#与Dirac算子之间的关系,并且给出了上述两个算子相等的一个条件.     

平移算子和调制算子的框架性质

连续框架是Hilbert空间中的一组向量, 它们能够利用连续叠加方式重构任意向量. 该文讨论了平移算子和调制算子所诱导的函数族的框架性质, 给出了它们不成为连续框架的条件.     

Structure of the repressor-operator complex of bacteriophage 434

The crystal structure of a specific complex between the DNA-binding domain of phage 434 repressor and a synthetic 434 operator DNA shows interactions that determine sequence-dependent affinity. The repressor recognizes its operators by its complementarity to a particular DNA conformation as well as by direct interaction with base pairs in the major groove.     

Dirichlet空间上总体紧的Toeplitz算子与Hankel算子

作者给出了Dirichlet空间上的算子序列为总体紧Toeplitz算子与Hankel算子的充分条件.     

酸碱软硬度的新标度研究

简要综述了Lewis酸碱软硬度定量标度的研究进展。在此基础上提出Lewis酸软硬度标度的改进方法，用离子键与共价键力之差（即HSA=Z/r^2i-Z*/r^2c)来计算Lewis酸的软硬性标度；引用新的电负性的计算方法，计算有关元素或基团的电负性（X），并将其结果用为Lewis碱的软硬性标度，扩大了Lewis碱的标度范围。此酸碱软硬度标度结果与Pearson对硬软酸碱的分类基本一致。     

重组质粒p434crohis的构建与表达

根据噬菌体４３４ｃｒｏ的基因序列,合成了一对在Ｃｒｏ的Ｃ－末端含有６个Ｈｉｓ密码子的寡核苷酸（６９ｂｐ）,并在其两端设计了ＰｓｔＩ和ＫａｓＩ两个酶切位点。经粘合、退火后将双股寡核苷酸链分别插入ｐ４３４ｃｒｏ（３．３５ｋｂ）质粒的４３８位（ＰｓｔＩ切点）和６３８位（ＫａｓＩ切点）,构建成含４３４ｃｒｏｈｉｓ基因的重组质粒。其表达产物为Ｃ端含有６个Ｈｉｓ的阻遏蛋白４３４ｃｒｏｈｉｓ。经功能测定表明融合蛋白４３４ｃｒｏｈｉｓ仍具有调节ＤＮＡ转录功能,并用金属亲和层析鉴定了表达产物     

积分算子与复合算子的本性交换性

算子的本性交换性是算子理论的重要组成部分,不同空间的复合算子与积分算子的乘积算子一般不是本性可交换的。给出了F(p,q,s)空间到加权Bloch空间的积分算子与复合算子的本性可交换的充分必要条件。     

耕播联合作业机的研究与设计

探讨了耕整、播种联合作业工艺,提出了适合我国北方的全幅旋耕、垄台碎茬、分层深施化肥、深松、开沟播种、扶垄或破垄和镇压等多种不同组合的耕整播种联合作业,并对系列耕整播种联合作业机的总体配置和主要工作部件进行了研究设计。