A point mutation in the neu oncogene mimics ligand induction of receptor aggregation

The rat neu gene, which encodes a protein closely related to the epidermal growth factor receptor, is a proto-oncogene that can be converted into an oncogene by a point mutation. Both genes encode proteins with a relative molecular mass of 185,000 but the question of why the neu gene product, p185neu, is oncogenic, whereas the product of c-neu, p185c-neu, is not, remains unanswered. The proteins have several features common to the family of tyrosine kinase growth-factor receptors, including cysteine-rich external domains, a hydrophobic transmembrane region and a cytoplasmic tyrosine kinase domain. The oncogenic p185neu differs from p185c-neu by an amino-acid substitution in the transmembrane region of the glycoprotein: this replacement of valine by glutamic acid at position 664 induces increased intrinsic tyrosine kinase activity which is associated with transformation. Many glycoproteins with charged amino acids in the transmembrane region exist as multimeric complexes at the plasma membrane. We have therefore investigated the association state of both products of the neu gene and show that the oncoprotein p185neu is organized at the plasma membrane primarily in an aggregated form, but that p185c-neu is not. Induction of an aggregated state may mimic aspects of ligand-induced receptor aggregation resulting in enzymatic activation that leads to cellular transformation.     

Genetic mechanisms of floral trait correlations in a natural population

Genetic correlations among traits are important in evolution, as they can constrain evolutionary change or reflect past selection for combinations of traits. Constraints and integration depend on whether the correlations are caused by pleiotropy or linkage disequilibrium, but these genetic mechanisms underlying correlations remain largely unknown in natural populations. Quantitative trait locus (QTL) mapping studies do not adequately address the mechanisms of within-population genetic correlations because they rely on crosses between distinct species, inbred lines or selected lines (see ref. 5), and they cannot distinguish moderate linkage disequilibrium from pleiotropy because they commonly rely on only one or two episodes of recombination. Here I report that after nine generations of enforced random mating (nine episodes of recombination), correlations between six floral traits in wild radish plants are unchanged, showing that pleiotropy generates the correlations. There is no evidence for linkage disequilibrium despite previous correlational selection acting on one functionally integrated pair of traits. This study provides direct evidence of the genetic mechanisms underlying correlations between quantitative traits in a natural population and suggests that there may be constraints on the independent evolution of pairs of highly correlated traits.     

白藜芦醇合酶基因的克隆及对毕赤酵母的转化

目的建立白藜芦醇合酶基因的毕赤酵母表达系统。方法通过PCR、限制性内切酶消化、连接、电激等方法,构建表达载体,转化毕赤酵母GS115。结果从葡萄基因组DNA中扩增得到了 1 200 bp目的基因,并克隆至pBS-T栽体;成功构建了表达载体pPIC3．5K／RS;目的基因成功整合进毕赤酵母GS115基因组中。测序及PCR鉴定证明,白藜芦醇合酶基因的毕赤酵母表达系统建立成功。结论所得方法无需高质量的RNA,从而降低了试验条件,达到了快速简便的目的。     

Association of a Ras-related protein with cytochrome b of human neutrophils

Activation of the superoxide generating system in human neutrophils is thought to involve the interaction or assembly of cytochrome b with other cytosolic and membrane proteins. We have now co-isolated by conventional purification procedures a protein of relative molecular mass 22,000 with cytochrome b. This Ras-related protein is not a fragment of either of the subunits of cytochrome b, and its primary structure, as determined by the sequencing of its complementary DNA, is identical to that predicted from a recently cloned ras-related gene, rap1 (also termed Krev-1). Immunoaffinity purification on anti-cytochrome and anti-Ras immunoaffinity matrices indicates an association between cytochrome b and the Ras-related protein. The association of a Ras-related GTP-binding protein with cytochrome b of human neutrophils could indicate a role for such a protein in the transduction, regulation or structure of the superoxide generating system.     

Association of tyrosine kinase p56lck with CD4 inhibits the induction of growth through the alpha beta T-cell receptor.

The membrane glycoprotein CD4 enhances antigen-mediated activation of T cells restricted by class II molecules of the major histocompatibility complex (MHC). This positive function has been attributed to the protein tyrosine kinase p56lck (ref. 4), which is noncovalently associated with the cytoplasmic portion of CD4, and is activated on CD4 aggregation. Antigen presentation by MHC class II molecules coaggregates CD4 and the T-cell antigen receptor (TCR alpha beta-CD3). Thus, the mutual specificity of CD4 and TCR alpha beta for the MHC-antigen complex results in the juxtaposition of p56lck and TCR alpha beta-CD3. In contrast, anti-CD4 antibodies can abrogate antigen-induced, as well as anti-TCR-induced T-cell activation, indicating that CD4 might also transduce negative signals. The molecular basis for this opposing function remains unclear. Here we show that the CD4-p56lck complex prohibits the induction of activation signals through the TCR-CD3 complex when not specifically included in the signalling process. This negative effect does not require anti-CD4 treatment, indicating that the induction of distinct negative signals is probably not involved. Rather, the results demonstrate that the CD4-p56lck complex provides prerequisite signals for antigen-receptor-induced T-cell growth and thus characterize a molecular mechanism for functional constraints imposed on T-cell activation by the MHC.     

一般容斥原理的数学归纳法证明

文中对一般容斥原理的数学公式q^{( n)}_k = p^{( n)}_k - C¹_k+1 p^{( n)}_k+1 + C²_k+2 p^{( n)}_k+2 - ⋯ ± C^{n - k}_n p^{( n)}_n = Σ ^{n- k}_α=0( -1) ^αC^α_k+αp^{( n)}_k+α进行了数学归纳法证明。     

酶法浸提酿酒葡萄果渣中多酚的最优工艺

以酿酒后葡萄果渣为原料,50%的乙醇溶液为介质,加入纤维素酶和果胶酶后,可浸泡提取葡萄果渣中多酚类物质.在不同酶浓度、pH值、反应温度和反应时间下进行单因素试验和正交试验,探讨不同条件对产率的影响,获得最优工艺条件.结果表明,保持反应温度55℃,在pH 5的条件下,加入浓度为4.5mg/g的混合酶(纤维素酶和果胶酶混合比例为1︰2)反应120min即可获得最大产率,与同条件下的无酶反应相比,产率提高了25.56%.     

葡萄籽油的提取和精炼工艺研究

对葡萄籽油提取和精炼工艺进行了研究.结果表明,在文中的试验条件下,葡萄籽油浸提最佳工艺条件是:石油醚为浸提剂,葡萄籽粒度60目、含水量7.0%、料液比1 g∶7 mL、温度70℃、浸提时间4h.葡萄籽油精炼工艺条件是:碱炼初温45℃,碱液浓度9.50%,超碱用量0.3%;水化加水量2%,水化时间分别为1.0、0.5 h;二次脱色工艺为活性脱色白土,加量第1次1%,脱色时间30 min、脱色温度80℃,第2次加量1%,脱色时间15 min,温度85℃,真空度0.08 MPa;在真空度0.08 MPa、温度180℃、脱臭时间1 h条件下可以脱除葡萄籽油中的臭味成分,保持葡萄籽的固有香味.     

变异率和种群数目自适应的遗传算法

提出了针对个体变异率和种群数目的2种自适应方法.算法中个体变异率根据其适度值在种群中的排序自适应调整,使优良个体具有较小的变异率继续进化,而使种群中较差个体具有较大变异率,增强了种群搜索能力.同时根据种群个体适度值方差动态调整变异率曲线,种群数目调整则根据最优个体更新率动态增大,以动态适应解空间的规模避免采样误差造成的进化停滞.通过在不同尺度的NK Landscape上与传统的简单遗传算法(SGA)比较可得,2种自适应方法的引入对遗传算法的寻优能力有了明显改进.