高必需氨基酸转基因马铃薯的研究

８０年代以来,马铃薯遗传转化系统日趋成熟,转基因工程植株已被广泛应用于基础科学研究［１］。作为食物蛋白和能量主要来源的马铃薯,提高其蛋白质含量及质量的遗传工程研究正受到人们的普遍关注［２］。Ｙａｎｇ等［２］将旨在改善氨基酸平衡的ＣＡＴ－ＨＥＡＡＥ（氯酶素乙酰转移酶－高含量人体必需氨基酸）融合基因导入马铃薯,获得了Ｓｏｕｔｈｅｒｎｂｌｏｔ、Ｎｏｒｔｈｅｒｎｂｌｏｔ、Ｗｅｓｔｅｒｎｂｌｏｔ的证据,但尚缺少氨基酸分析的资料。玉米醇溶蛋白（ｚｅｉｎ）［３］是一个富含甲硫氨酸的贮存蛋白,它和人工合成的ＨＥ…     

Proton-induced membrane fusion role of phospholipid composition and protein-mediated intermembrane contact

Glycolipid-phospholipid vesicles containing phosphatidate and phosphatidylethanolamine were found to undergo proton-induced fusion upon acidification of the suspending medium from pH 7.4 to pH 6.5 or lower, as determined by an assay for lipid intermixing based on fluorescence resonance energy transfer. Lectinmediated contact between the vesicles was required for fusion. Incorporation of phosphatidylcholine in the vesicles inhibited proton-induced fusion. Vesicles in which phosphatidate was replaced by phosphatidylserine underwent fusion only when pH was reduced below 4.5, while no significant fusion occured (pH ? 3.5) when the anionic phospholipid was phosphatidylinositol. It is suggested that partial protonation of the polar headgroup of phosphatidate and phosphatidylserine, respectively, causes a sufficient reduction in the polarity and hydration of the vesicle surface to trigger fusion at sites of intermembrane contact.     

Effects of bovine parathyroid hormone and 1,25-dihydroxyvitamin D3 on the production of prostaglandins by cells derived from human bone

Local production of prostaglandins by osteoblasts may be important in controlling the bone resorbing activity of some hormones which have receptors on osteoblasts. We have demonstrated that osteoblast-like cells derived from human bone can incorporate [14C]arachidonic acid into phospholipids and synthesise immunoreactive PGE. Parathyroid hormone increases both the release of incorporated arachidonic acid and the synthesis of PGE. This is the first demonstration of modulation of bone cell prostaglandin synthesis by a bone resorbing hormone.     

Progress in cellular engineering of plants: biochemical and genetic assessment of selectable markers from cultured cells

Summary Recent availability of stable and well characterized selectable markers and ability to combine alien genomes parasexually have contributed to the development of molecular biology in higher plants, including gene expression and genetic manipulation.Several types of biochemical mutants (resistant to inhibitory concentrations of aminoacid(s) or aminoacid analogs as well as deficient for enzyme activity) have recently been isolated and characterized biochemically and genetically. Among them, mutants with alterations in the nitrogen and aminoacid metabolism, or in the activity of alcohol dehydrogenases are being used in the development of more efficient techniques of gene transfer.The manipulation of whole genomes by sexual or somatic cell fusion offers new potential in this field, but refinement of transfer techniques is desirable. The new set of selectable markers obtained through advanced cellular technology, as well as our ability to regenerate plants from manipulated cell lines are expected to play a major role in cellular engineering.     

Fusion of phosphatidylserine and mixed phosphatidylserine-phosphatidylcholine vesicles Dependence on calcium concentration and temperature

Dynamic light scattering has been used to study the temperature dependence of Ca²⁺-induced fusion of phosphatidylserine vesicles and mixed vesicles containing phosphatidylserine and different phosphatidylcholines. The final vesicle size after Ca²⁺ and EDTA incubation serves as a measure of the extent of fusion. With phosphatidylserine vesicles, the extent of fusion shows a sharp maximum at an incubation temperature which depends on the Ca²⁺ concentration between 0.8 and 2 mM. The shift in the fusion peak temperature with Ca²⁺ concentration is similar to the typical shift in the phase transition temperature with divalent cation concentration in acidic phospholipids. The results suggest a direct correlation between the fusion peak temperature and the phase transition temperature in the presence of Ca²⁺ prior to fusion. With mixed vesicles containing up to 33% of a phosphatidylcholine in at least 2 mM Ca²⁺, the extent of fusion as a function of incubation temperature also shows a maximum. The fusion peak temperature is essentially independent of the quantity and type of phosphatidylcholine and the Ca²⁺ concentration, and identical to that with pure phosphatidylserine in excess Ca²⁺. The results imply that Ca²⁺-induced molecular segregation occurs first, and fusion subsequently takes place between pure phosphatidylserine domains.     

Fusion of phosphatidic acid-phosphatidylcholine mixed lipid vesicles

Ca²⁺-induced transformation of phosphatidylcholine-phosphatidic acid vesicles to larger bilayer structures has been examined using nuclear magnetic resonance, electron microscopy, gel permeation and radioisotope tracer techniques. For concentrated vesicle preparations where phosphatidic acid content remains less than 50% of total lipid, transformation to larger well defined unilamellar structures can be induced. The size of the product formed is dependent on phosphatidic acid content and on Ca²⁺ content when Ca²⁺ levels are between 0.3 and 1.0 mol ratios with respect to phosphatidic acid. During transformation bilayer composition remains unchanged and internal contents are retained in the final structure. These properties are indicative of concerted two vesicle and multiple vesicle fusions. The controllable and concerted fusions make the phosphatidic acid system suitable for further mechanistic studies.     

Studies on antiviral glycosides. II. Mode of action for virucidal effects on Sendai virus

Treatment of Sendai virus with $\text{p-(sec-}\text{butyl)-phenyl-6-chloro-6-deoxy-β-}\text{d}\text{-glucopyranoside}$, followed by freezing and thawing resulted in a loss of hemolytic and cell fusion activities as well as infectivity without affecting hemagglutinating and neuraminidase activities. The anti-hemolytic activity of this compound was reversed by the addition of phosphatidyl choline to the virus samples. $\text{p-}\text{Azidophenyl-6-chloro-6-deoxy-β-}\text{d}\text{-[}{}^3\text{H]glucopyranoside}$ was successfully used for photoaffinity labeling of a specific virion site, and we confirmed the affected site of the glucoside to be the lipid components in the viral envelopes.     

Effects of microtubule-disruptive and membrane-stabilizing agents on low density lipoprotein metabolism by cultured human fibroblasts

The cellular mechanisms involved in the uptake and metabolism of low density lipoprotein (LDL) by cultured normal human fibroblasts have been investigated with the aid of drugs known to disrupt cytoplasmic microtubules or to inhibit membrane fusion.Two drugs which disrupt microtubules by differing mechanisms, colchicine and vinblastine, each reduced the high affinity surface binding of ¹²⁵I-labelled LDL by fibroblasts. Associated reductions of the endocytosis and degradation of the lipoprotein could be attributed almost entirely to this effect. In contrast, lumicolchicine, an analogue of colchicine without microtubule-disruptive activity, had little or no effect on ¹²⁵I-labelled LDL metabolism.Each of two groups of membrane-stabilizing agents, the phenothiazines and the tertiary amine local anaesthetics, directly inhibited both the internalization of ¹²⁵I-labelled LDL following high affinity binding to cell surface receptors and the catabolism of the lipoprotein subsequent to endocytosis, supporting previous morphological evidence for the importance of membrane fusion in these processes.     

Redistribution of intramembrane particles of human erythrocytes induced by HVJ (Sendai virus): A prerequisite for the virus-induced cell fusion

Aggregation of intramembrane particles of human erythrocytes was found to be induced by HVJ (Sendai virus) under conditions which lead to cell fusion. Degree of polyerythrocyte formation was compared under a variety of conditions with extent of cluster formation observed with the same preparations. Both structural changes of the membranes, ie, fusion and clustering of the particles, behaved very similarly under widely different virus-to-cell ratios and over the time course of cell fusion. Furthermore, by inclusion of high concentrations of antispectrin antibodies within the ghosts, inhibition of clustering of intramembrane particles and hindrance of virus-induced cell fusion were found to occur simultaneously. Antibodies by themselves did not induce aggregation of particles under isotonic conditions, whereas particle clustering could be induced under hypotonic conditions at antibody concentrations causing partial cross-linking of spectrin molecules. In conclusion, clustering of intramembrane particles seems to be required for virus-induced fusion of human erythrocytes.     

Changements de l'epithélium médian des bourgeons palatins de souris au stade de préfusion

Résumé Avant d'entrer en contact, les surfaces de fusion des processus palatins subissent des modifications. Certaines cellules épithéliales superficielles deviennent turgescentes, alors que d'autres conservent un aspect dense et aplati, elles se lysent et éclatent. Des noyaux semblables à ceux des assises profondes se retrouvent en surface, paraissant migrer vers le bourgeon antagoniste. Des projections filamenteuses apparaissent, quelques unes établissant un contact avec l'épithélium opposé, d'autres restant seulement sous forme d'expansion. Ces observations sont concordantes en microscopie photonique et en microscopie électronique à balayage.

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Modification of the medial epithelium of the palatal shelves of mice at the prefusion stage. A light and scanning electron microscopy study

Summary The fusion surfaces of the palatal processes are modified before coming into contact. Several superficial epithelial cells become hypertrophied, undergo lysis and burst, whereas others remain flattened and densely stained. Nuclei, similar to those localized in deeper layers are found on the surface and seem to migrate towards the opposite process. Filamentous projections appear and some establish a linkage with the opposite epithelium, whereas others expand freely from the surface. Light microscope observations agree with scanning electron microscopy findings.