Probing met repressor-operator recognition in solution.

The three-dimensional crystal structure of the Escherichia coli methionine repressor, MetJ, complexed with a DNA operator fragment is described in an accompanying article. The complex exhibits several novel features of DNA-protein interaction. DNA sequence recognition is achieved largely by hydrogen-bond contacts between the bases and amino-acid side chains located on a beta-ribbon, a mode of recognition previously hypothesized on the basis of modelling of idealized beta-strands and DNA, and mutagenesis of the Salmonella phage P22 repressors Arc and Mnt. The complex comprises a pair of MetJ repressor dimers which bind to adjacent met-box sites on the DNA, and contact each other by means of a pair of antiparallel alpha-helices. Here we assess the importance of these contacts, and also of contacts that would be made between the C-helices of the protein and DNA in a previous model of the complex, by studying mutations aimed at disrupting them. The role of the carboxy-terminal helix face in operator binding was unclear, but we demonstrate that recognition of operator sequences occurs through side chains in the beta-strand motif and that dimer-dimer interactions are required for effective repression.     

热力学基本不等式包含的不可逆过程

利用把系统外参量和内参量分开的方法，给出了热力学基本方程的表示式；分析了各个热力学基本不等式包含的不可逆过程；讨论了热力学基本不等式的适用条件．为热力学理论的广泛应用提供了理论依据     

生长调节剂对大叶白蜡幼苗生长的影响

对一年生大叶白蜡实生苗用3种不同浓度的赤霉素（GA3）、ABT生根粉7号（ABT7）、萘乙酸（NAA）进行处理。结果表明，3种生长调节剂对大叶白蜡幼苗生长有明显的促进作用。处理后的苗木提高，生长加快，茎干增粗，叶片增大，抗性增强，其中以50mg/L的GA3作用最为显著。     

Activation of a C. elegans Antennapedia homologue in migrating cells controls their direction of migration.

Anterior-posterior patterning in insects, vertebrates and nematodes involves members of conserved Antennapedia-class homeobox gene clusters (HOM-C) that are thought to give specific body regions their identities. The effects of these genes on region-specific body structures have been described extensively, particularly in Drosophila, but little is known about how HOM-C genes affect the behaviours of cells that migrate into their domains of function. In Caenorhabditis elegans, the Antennapedia-like HOM-C gene mab-5 not only specifies postembryonic fates of cells in a posterior body region, but also influences the migration of mesodermal and neural cells that move through this region. Here we show that as one neuroblast migrates into this posterior region, it switches on mab-5 gene expression; mab-5 then acts as a developmental switch to control the migratory behaviour of the neuroblast descendants. HOM-C genes can therefore not only direct region-specific patterns of cell division and differentiation, but can also act within migrating cells to programme region-specific migratory behaviour.     

关于职校生期刊的办刊特色研究

职校生期刊是随着我国经济建设和职教事业飞速发展而崛起的一支传媒新军。文稿就期刊的办刊方针、刊载内容、版式设计以及服务意识作了探索,凸现了期刊为职校生读者群服务的个性特色。     

Heterostructure in ZnO Nano-Tetrapods

1 Introduction 　　Nanoscale science and technology have attracted greatattention since the novel properties become dominant for well-known materials as their sizes reduced to some critical dimension. These properties frequently originate in lattice distortions, structure transformations etc[1]. The variations of size and structure ofnanocrystals lead to the change of their electronic structures. Very recently, nanoscale materials with different electronic structures were utilized in fabricating nanoscale junctions[2]. 　　……     

峡江方言的人称代词

峡江方言的人称代词主要有三身代词我、你、渠、我叽、我吧、你叽、渠叽以及非三身代词自家、口口[p‘iaη~(44)·ηa]、人家、大家。全文对它们的语音形式作了详细描写,并通过与普通话中的相应形式的比较,逐个分析它们的意义指称对象和语法功能,其中有些人称代词在语用中还会发生转义,文中将其概括为虚指、泛指和转指三种情况。