四膜虫中存在角蛋白样成分(简报)

中等纤维是脊椎动物细胞中普遍存在的一种细胞骨架成分,在一些无脊椎动物细胞中也发现有这类成分存在。据报道,枪乌贼的巨     

微核形成与细胞周期关系的初步研究 Ⅲ.丝裂霉素c诱发人淋巴细胞染色体畸变与不同周期阶段的微核形成

为了研究染色体畸变与微核形成的关系,本实验用不同浓度的丝裂霉素C(MMC,0.025—0.4μg/ml),处理人外周血淋巴细胞,观察中期染色体畸变与不同细胞周期形成的微核间的关系。获得如下主要结果:(1)MMC诱发的染色体畸变细胞率(ACF),未经培养的G_0期淋巴细胞的微核细胞率(NC-MNCF)以及培养的淋巴细胞的微核细胞率(C-MNCF),在一定剂量范围内均呈剂量依赖性增加,并可用幂回归方程描述;(2)微核形成与染色体畸变全然无关的NC-MNCF,和C-MNCF一样,与ACF呈良好的正相关;(3)用胞质分裂阻滞(CB)法,检测MMC诱发的CB-MNCF,较C-MNCF无显著提高,MNCF/ACF的比值较小,并随着MMC剂量增加从0.15左右降到0.03。所有上述结果表明,不能简单理解微核形成与染色体畸变间的关系,在分裂的细胞群体中,中期染色体畸变可能仅是微核形成的一种来源。     

云南10个民族红细胞酸性磷酸酶型分布调查

用淀粉凝胶电泳法对云南省汉族及9个少数民族的红细胞酸性磷酸酶(ACP_1)的表型分布进行了调查,检出A、BA和B3种表型,计算得云南汉、彝、白、傣、瑶、佤、哈尼、布朗、基诺和拉祜族ACP_1~A、ACP_1~B的基因频率依次为0.2067、0.7933;0.2406、0.7594;0.2341、0.7659;0.3750、0.6250;0.2300、0.7700;0.2727、0.7273;0.3594、0.6406;0.3036、0.6964;0.2381、0.76119和0.4474、0.5526。未发现ACP_1~C基因及其它稀有基因。研究表明,ACP_1表型的分布存在着一定的种族与民族差异。     

Molecular genetic, biochemical and nuclear magnetic resonance studies on the role of the tryptophan residues of glutamine-binding protein from Escherichia coli

The results of molecular genetic, biochemical and nuclear magnetic resonance studies on glutamine-binding protein of Escherichia coli suggest that the only two tryptophan residues, at positions 32 and 220, in the protein molecule are likely to be involved in (or sensitive to) interactions with the membrane-bound protein components of the glutamine transport system. It has been found that both tryptophan residues have limited motional freedom, are located away from the surface of the protein molecule and are not close to the ligand-binding site. Their presence, however, is required for the optimal transport of L-glutamine across the cytoplasmic membrane, though not essential for the ligand-binding process. The relevance of these results to the structure and function of the glutamine-binding protein in the glutamine transport system is discussed.     

The potential role of DNA methylation in the response to 2,3,7,8-tetrachlorodibenzo-p-dioxin

The Ah receptor is an intracellular protein that binds the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin. The liganded receptor interacts with a specific DNA recognition motif located within a dioxin-responsive enhancer upstream of the CYP1A1 gene. Methylation protection and methylation interference studies indicate that the liganded receptor contacts both DNA strands, at 4 guanine residues contained within the recognition motif. These findings imply that the liganded receptor interacts with its cognate enhancer within the major groove of the DNA helix. Cytosine methylation of the recognition motif at CpG dinucleotides diminishes the protein-DNA interaction, as measured by gel retardation. Furthermore, methylation at cytosine inhibits the enhancer function of the DNA. These findings imply that DNA methylation can diminish the response to dioxin by impeding the Ah receptor-enhancer interaction.     

Subcellular distribution of the 1,4-dihydropyridine receptor in rabbit skeletal muscle in situ: an immunofluorescence and immunocolloidal gold- labeling study

The subcellular distribution of the 1,4-dihydropyridine receptor was determined in rabbit skeletal muscle in situ by immunofluorescence and immunoelectron microscopy. Longitudinal and transverse cryosections (5-8 microns) of rabbit gracilis muscle were labeled with monoclonal antibodies specific against either the alpha 1-subunit (170,000-D polypeptide) or the beta-subunit (52,000-D polypeptide) of the 1,4-dihydropyridine receptor by immunofluorescence labeling. In longitudinal sections, specific labeling was present only near the interface between the A- and I-band regions of the sarcomeres. In transverse sections, specific labeling showed a hexagonal staining pattern within each myofiber however, the relative staining intensity of the type II (fast) fibers was judged to be three- to fourfold higher than that of the type I (slow) fibers. Specific immunofluorescence labeling of the sarcolemma was not observed in either longitudinal or transverse sections. These results are consistent with the idea that the alpha 1-subunit and the beta-subunit of the purified 1,4-dihydropyridine receptor are densely distributed in the transverse tubular membrane. Immunoelectron microscopical localization with a monoclonal antibody to the alpha 1-subunit of the 1,4-dihydropyridine receptor showed that the 1,4-dihydropyridine receptor is densely distributed in the transverse tubular membrane. Approximately half of these were distributed in close proximity to the junctional region between the transverse tubules and the terminal cisternae. Specific labeling was also present in discrete foci in the subsarcolemmal region of the myofibers. The size and the nonrandom distribution of these foci in the subsarcolemmal region support the possibility that they correspond to invaginations from the sarcolemma called caveolae. In conclusion, our results demonstrate that the 1,4-dihydropyridine receptor in skeletal muscle is localized to the transverse tubular membrane and discrete foci in the subsarcolemmal region, possibly caveolae but absent from the lateral portion of the sarcolemma.     

Cause for dark, chilling-induced inactivation of photosynthetic oxygen-evolving system in cucumber leaves

Effects on oxygen evolution of the storage of detached cucumber (Cucumis sativus) leaves at 0°C in the dark were investigated with thylakoids and oxygen-evolving photosystem II membranes isolated from stored leaves. The cold and dark treatment of leaves selectively inactivated electron transport on the oxidizing side of photosystem II. Photosystem II membranes isolated from treated leaves were largely depleted of two proteins of 20 and 14 kilodaltons, which correspond to the extrinsic 23- and 17- kilodalton proteins of spinach functioning in oxygen evolution. The manganese content of photosystem II membranes was also markedly reduced by the treatment. Thus, the inactivation of oxygen evolution induced by the dark, chilling treatment is ascribed to solubilization of the 20- and 14-kilodalton proteins and extraction of manganese.     

白细胞介素2受体α链基因转录起始点和5'调控区结合蛋白的初步研究

 借助于5'和3'末端删切后重建的IL-2R a链基因调控区次级克隆,在体外合成有放射性同位素参入的反意义RNA探针与总RNA进行液相杂交,结果表明TPA或PHA分别活化的T细胞在IL-2R a链表达过程中都在不同程度上有选择地利用了调控区内分别为-58(5')和+1(3')位两个转录起始点中3'转录起始点。热休克使PHA活化细胞更明显地利用+1位点。PHA诱导Jurkat细胞表达IL-2RamRNA斑点杂交证实,Jurkat细胞在活化16小时表达IL-2Ra基本达到高峰,至24小时已明显下降。根据这一规律提取PHA诱导活化15小时的Jurkat细胞S100和NE,进行有关结合蛋白的研究,初步结果显示磷酸纤维素柱的KCI洗脱组分中存在着DNA结合蛋白,有关结合蛋白性质的研究正在进行中。     

Short-fibre formation during cellulose degradation by cellulolytic fungi

Summary All cell-free filtrates of 26 fungal strains containning cellulase activities degraded native cellulose to both reducing sugar and insoluble short fibres. Low-molecular components from the crude filtrates could also degrade native cellulose into short fibres, not accompanied with the production of reducing sugar. Short fibre formation played an important role in cellulose degradation to make the substrate more accessible to attack of cellulases.