光弹性法和焦散线法研究联结零件接触应力

采用经典的三维光弹性实验技术和新兴的焦散线实验方法，分别研究了螺栓联结件的三维接触应力及其接触影响区域。所得实验结果为汽缸盖接触联结系统的设计、机械螺栓联结零件的有限元计算及其可靠性分析，提供了实验依据，并开拓了焦散线法实验的应用范围。     

Presynaptic release probability influences the locus of long-term potentiation.

The quantal hypothesis proposes that chemical synaptic transmission involves the probabilistic release of multimolecular packets of transmitter. Analysis of the resulting trial-to-trial fluctuations in postsynaptic response can provide estimates both of the number of quanta released and of the size of their postsynaptic effect. This in turn permits the quantification of the relative contributions of pre- and postsynaptic factors to the strength of a given synapse. Quantal analysis of excitatory synapses in the hippocampus has proved difficult and has led to contradictory conclusions when applied to long-term potentiation. Here we report the use of a combination of quantal analysis procedures to provide evidence that both pre- and postsynaptic changes can contribute substantially to the maintenance of long-term potentiation in the CA1 region of the hippocampus. The initial setting of the presynaptic release mechanism seems to determine their relative importance.     

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.     

Sequence homology of the LFA-1 and Mac-1 leukocyte adhesion glycoproteins and unexpected relation to leukocyte interferon

Cell-surface adherence reactions are fundamental to the biology of lymphocytes, monocytes and granulocytes. The lymphocyte function-associated 1 (LFA-1) and macrophage 1 (Mac-1) glycoproteins mediate differing types of adhesion reactions on these cells. LFA-1 participates in T-lymphocyte and natural killer-cell adhesion to target cells, whereas the Mac-1 antigen is identical to the complement receptor type 3, which mediates adhesion of monocytes and granulocytes to C3bi-sensitized particles. Deficiency of these proteins, in a heritable disease, results in multiple adhesion-related leukocyte defects. LFA-1 and Mac-1 resemble one another in overall structure, having alpha-subunits of relative molecular mass (Mr) 180,000 and 170,000, respectively, which are non-covalently associated with beta-subunits of Mr 95,000 in alpha 1 beta 1 complexes. Peptide mapping and immunological cross-reactivity have shown that the beta-subunits are highly related if not identical, but have revealed no similarities between the alpha-subunits. Nonetheless, the shared beta-subunit suggested that LFA-1 and Mac-1 might be members of a protein family containing diversified but evolutionarily related alpha-subunits. Therefore, we examine here the structure of the alpha-subunits by N-terminal amino-acid sequencing. Sequence homology shows that the alpha-subunits are members of a novel leukocyte adhesion protein family, and suggests that their evolution occurred by gene duplication. A search for similarities to previously sequenced proteins reveals a further unexpected homology between LFA-1 and leukocyte (alpha) interferons.     

Structure, expression and divergence of T-cell receptor beta-chain variable regions

Analysis of three new T-cell receptor beta-chain variable regions together with those in the literature indicates that they have both remarkable similarities and differences with those of immunoglobulin. Less than 10 V regions appear to predominate in the thymus. V beta sequences are much more heterogeneous at the amino acid level than are immunoglobulin V regions and they appear to diverge between species much more quickly, apparently the result of additional hypervariable regions. Three of these putative new hypervariable regions lie outside of the classical immunoglobulin binding site, an indication that important interactions may be occurring in these regions with polymorphic MHC determinants.