Bicyclonucleosides and ring-chain interconversion.

Four types of bicyclonucleosides differing in the easiness of their ring-chain interconversion have been prepared, some exhibited anti-HIV activity and the ratio of their cyclic and open-chain forms could have some bearing on their biological activity.     

Bicyclonucleosides and Ring-Chain Interconversion

Abstract

Four types of bicyclonucleosides differing in the easiness of their ring-chain interconversion have been prepared. some exhibited anti-HIV activity and the ratio of their cyclic and open-chain forms could have some bearing on their biological actitity.     

植物对荒漠生境的趋同适应

植物体的表型特征是其基因与生态因子二者共同作用的结果,生活在荒漠生境中的植物由于遭受相同的自然选择压力,在外部形态、内部结构、生活史特征、生理特性、次生代谢产物的合成以及大分子物质的诱导产生等诸多表型方面均表现出高度趋同的现象。随着研究手段的改善,对植物趋同适应的研究已逐渐深入到了分子水平。研究荒漠生境中植物的趋同适应对于人们深刻地认识和理解植物与环境间的相互关系及其分子基础,以及利用功能基因改良重要作物的抗逆性等将会产生深远的影响;对极端干旱环境下特殊次生代谢产物的定向发现及重要先导化合物的筛选等有着重大的指导意义;同时对我国的西部开发及干旱区的生态恢复亦有重要的参考价值。     

猕猴桃茎尖超低温保存过程中超微结构观察

应用透射电镜观察了猕猴桃组培苗茎尖细胞在玻璃化法超低温保存过程中的超微结构变化.研究发现:在预培养、PVS2脱水处理过程中,茎尖细胞内液泡逐渐变多、变小,质壁分离愈加显著,表明细胞的抗冻力增强;在随后的冷冻和解冻过程中,部分细胞的质壁分离更加严重,细胞壁与细胞膜之间出现液腔,细胞器变得模糊,有些细胞的细胞膜、甚至细胞壁撕裂,细胞腔内留下破碎的细胞膜和细胞残片,细胞结构破坏严重,这可能是导致材料在恢复培养中死亡的原因之一;部分细胞经过7d的恢复培养后,细胞器清晰,细胞膜完好并紧贴细胞壁,细胞中央出现较大的液胞,具有与对照相似的结构特征,最终存活下来并能够再生植株.     

天然免疫抗病毒效应分子Mx蛋白的结构与功能研究进展

Mx蛋白是很多物种中干扰素诱导的抗病毒状态的关键成分.它们是一类动素样GTPase,具有类似动素的结构和功能特点,例如自我组装以及和细胞内膜结合.Mx蛋白独特的性质使其具有广泛的抗病毒活性,它们作用于病毒进入细胞后不久、病毒基因组复制之前,抑制病毒复制周期的早期阶段.已知一些Mx蛋白识别病毒的核衣壳成分,干扰病毒基因组的复制.动素家族某些成员的晶体结构已经得到解析,解析Mx蛋白的晶体结构对理解其抗病毒机制以及防治新生突发病毒有重要意义.     

Strategies for successful recombinant expression of disulfide bond-dependent proteins in Escherichia coli

Bacteria are simple and cost effective hosts for producing recombinant proteins. However, their physiological features may limit their use for obtaining in native form proteins of some specific structural classes, such as for instance polypeptides that undergo extensive post-translational modifications. To some extent, also the production of proteins that depending on disulfide bridges for their stability has been considered difficult in E. coli.     

Virus Entry, Assembly, Budding, and Membrane Rafts

As intracellular parasites, viruses rely heavily on the use of numerous cellular machineries for completion of their replication cycle. The recent discovery of the heterogeneous distribution of the various lipids within cell membranes has led to the proposal that sphingolipids and cholesterol tend to segregate in microdomains called membrane rafts. The involvement of membrane rafts in biosynthetic traffic, signal transduction, and endocytosis has suggested that viruses may also take advantage of rafts for completion of some steps of their replication cycle, such as entry into their cell host, assembly, and budding. In this review, we have attempted to delineate all the reliable data sustaining this hypothesis and to build some models of how rafts are used as platforms for assembly of some viruses. Indeed, if in many cases a formal proof of raft involvement in a virus replication cycle is still lacking, one can reasonably suggest that, owing to their ability to specifically attract some proteins, lipid microdomains provide a particular milieu suitable for increasing the efficiency of many protein-protein interactions which are crucial for virus infection and growth.     

Virus entry, assembly, budding, and membrane rafts.

As intracellular parasites, viruses rely heavily on the use of numerous cellular machineries for completion of their replication cycle. The recent discovery of the heterogeneous distribution of the various lipids within cell membranes has led to the proposal that sphingolipids and cholesterol tend to segregate in microdomains called membrane rafts. The involvement of membrane rafts in biosynthetic traffic, signal transduction, and endocytosis has suggested that viruses may also take advantage of rafts for completion of some steps of their replication cycle, such as entry into their cell host, assembly, and budding. In this review, we have attempted to delineate all the reliable data sustaining this hypothesis and to build some models of how rafts are used as platforms for assembly of some viruses. Indeed, if in many cases a formal proof of raft involvement in a virus replication cycle is still lacking, one can reasonably suggest that, owing to their ability to specifically attract some proteins, lipid microdomains provide a particular milieu suitable for increasing the efficiency of many protein-protein interactions which are crucial for virus infection and growth.     

What do European badgers (Meles meles) know about the spatial organisation of neighbouring groups?

European badgers (Meles meles) live in groups. Although they can distinguish between a member of their own group, a member of a neighbouring group and a stranger, their ability to understand that neighbouring individuals belong to different groups inhabiting different places, and possibly to build up some representation of the spatial organisation of neighbouring groups remains to be shown. In this study, we conducted a pilot homing experiment to test such ability. Radio-collared badgers were displaced to the home ranges of neighbouring groups and their homing performances were compared to those of badgers displaced either to the periphery of their own group's home range or beyond the neighbouring home ranges. When released in their own home range, badgers homed rapidly and efficiently, whereas when released beyond the neighbouring groups' home ranges (whatever the distance) they did not home. In contrast, badgers released in the home range of a neighbouring group performed some random search there, before returning to their setts quite efficiently. These results suggest that badgers may consider their neighbours as members of different groups inhabiting different places close to their own home range, but their ability to build up some spatial representation of neighbourhood relationships could not be demonstrated.     

Developmental tumours, early differentiation and the transforming growth factor beta superfamily

Embryonal carcinoma and embryonic stem cells have been very useful models for identifying some of the factors that regulate differentiation in early mammalian development. Here, we present a brief history of their original isolation and characterization and of their later introduction into the Hubrecht Laboratory. We illustrate in a review their contribution to our current understanding of the function of transforming growth factor beta and ligands binding to the receptors of a related factor, activin, in development with some of our own work.     

Modulating the activity of neural crest regulatory factors

Substantial progress has been made in defining the regulatory factors involved in generating multipotent neural crest cells at the neural plate border of vertebrate embryos, controlling the onset of their migratory behavior, and directing their differentiation into one of a diverse array of derivatives. Growing evidence suggests that these factors function as a complex network, in some cases displaying overlapping functions and cross-regulatory interactions. Mechanisms are emerging for how some of these regulatory components are controlled post-translationally and the extent to which their activities are conserved across species.     

植物人工异源多倍体的遗传及后遗传变化

据估计,70%以上的显花植物在其生活史上至少发生过一次以上的多倍化。传统的有关多倍性的观点认为,多倍体基因组应是其双亲基因组的积加。但是,有些合成异源多倍体的基因组发生了广泛的遗传及后遗传变化。这些变化包括亲本DNA序列丢失、核仁显性、DNA甲基化模式改变、基因沉默、反转座子激活等。亲本序列丢失可能与部分同源序列间重组有关,而亲本基因沉默可能与同源性依赖的基因沉默及RNA干涉等有关。     

近自然纯培养法对细菌培养的初步研究

依据微生物在自然生境中协作生长的基本特性,提出一种对传统纯培养技术的改进思路及方法：设计一种有孔培养皿,皿内覆盖有不允许细菌通过、但营养物质可以自由流动的微孔滤膜。培养时将该培养皿放入被分离微生物所需生境中,可以克服传统纯培养难以提供外源活性物质的缺陷,一定程度上弥补了混合培养法和传统纯培养法的弱点,从而达到增强部分微生物可培养性、甚至培养出未培养微生物的目的。     

Antimicrobial activities of some Bacillus spp. strains isolated from the soil

In this study a total of 29 Bacillus species isolated from the soil was analyzed using the agar diffusion method in terms of their general inhibition effects to some test bacteria. It has been found that isolates are effective against gram-positive and gram-negative bacteria whereas their extensive inhibition effect is particularly against gram-positive bacteria. On the other hand, B. cereus M15 strain has an inhibitory effect against both gram-positive and gram-negative bacteria. Furthermore some isolates are more effective against test bacteria when compared to some antibiotics.     

An adaptive feature of some mangroves of Sundarbans, West Bengal

Mangrove taxa, apart from their morphological characters, have some unique leaf anatomical features which are very much related to their adaptation as the plants grow in unstable, variable and saline environments with regular tidal influence. Special stomatal structures with extended cuticles render the transpiration rate in many taxa. The presence of glandular and non-glandular hairs on the abaxial and/or adaxial leaf surfaces in some taxa are related to salt secretion of these plants. Comparatively large amounts of water storage tissues occur in the hypodermal or mesophyll tissue of the leaves, reflecting the adaptive nature of mangroves in their stressful habitat. The occurrence of terminal tracheids helps with capillary water storage within the leaf. The coriaceous nature of the leaves in some taxa is due to the presence of sclereids within the mesophyll region. It is noted thatHeritiera is unsuitable to the highly saline habitat of the Sundarbans forest region because of some anatomical peculiarities.     

Isolation of Clostridium difficile from stored specimens and comparative susceptibility of various tissue culture cell lines to cytotoxin

Abstract Toxins A and B of Clostridium difficile were purified to homogeneity and some of their properties were examined. The toxins have similar LD₁₀₀ values in mice, share some similarities in their amino acid composition, and are both sensitive to oxidizing agents. However, they have different isoelectric points and do not show any significant peptide homology.     

Primates as pets in Mexico City: an assessment of the species involved, source of origin, and general aspects of treatment

The large human populations in cities are an important source of demand for wildlife pets, including primates, and not much is known about the primate species involved in terms of their general origin, the length of time they are kept as pets, and some of the maintenance problems encountered with their use as pets. We report the results of a survey conducted in Mexico City among primate pet owners, which was aimed at providing some of the above information. We used an ethnographic approach, and pet owners were treated as informants to gain their trust so that we could enter their homes and learn about the life of their primate pets. We surveyed 179 owners of primate pets, which included 12 primate species. Of these, three were native species (Ateles geoffroyi, Alouatta pigra, and A. palliata). The rest were other neotropical primate species not native to Mexico, and some paleotropical species. Spider monkeys and two species of howler monkeys native to Mexico accounted for 67% and 15%, respectively, of the primate cases investigated. The most expensive primate pets were those imported from abroad, while the least expensive were the Mexican species. About 45% of the native primate pets were obtained by their owners in a large market in Mexico City, and the rest were obtained in southern Mexico. Although they can provide companionship for children and adults, primate pets are subject to a number of hazards, some of which put their lives at risk. The demand by city dwellers for primate pets, along with habitat destruction and fragmentation, exerts a significant pressure on wild populations in southern Mexico.     

Mechanisms of stage-regulated gene expression in kinetoplastida

During their life cycle, trypanosomatid parasites of mammals encounter substantially different environments in their hosts and insect vectors, to which they must adapt by undergoing a series of differentiation processes. At the molecular level, these processes must be the direct result of an elaborate series of changes in stage-regulated expression of a wide range of gene products. How are these changes accomplished? In this review, Sheila Graham discusses some recent advances in understanding the mechanisms of gene expression in trypanosomatids, and examines some clues to some intriguingly complex means of regulating life cycle stage-specific gene expression.     

RDMAS: a web server for RNA deleterious mutation analysis

Background  

The diverse functions of ncRNAs critically depend on their structures. Mutations in ncRNAs disrupting the structures of functional sites are expected to be deleterious. RNA deleterious mutations have attracted wide attentions because some of them in cells result in serious disease, and some others in microbes influence their fitness.