神经营养因子功能的“阴/阳”特性

神经营养因子是一类对神经元的营养、支持、分化及突触可塑性等具有重要作用的蛋白质。近年来研究发现神经营养因子合成中的前体分子产生相反的诱导神经元凋亡作用,并在中枢退行性疾病发生中扮演着重要的角色。本文综述了神经营养因子及其前体蛋白在合成代谢、受体调控和功能上的"阴/阳"特性,并讨论其在疾病过程中的可能作用,为进一步探索认识神经营养因子的功能、病理意义、疾病治疗价值提供新的视角。     

Overexpression of the 3'-untranslated region of myelin proteolipid protein mRNA leads to reduced expression of endogenous proteolipid mRNA

The current studies focus on what mechanisms regulate the concentration of PLP mRNA in cells. The PLP mRNA is very stable and these studies suggest that its stability is regulated by a trans-acting factor specific to oligodendrocytes. In order to test whether the 3untranslated region (3UTR) of the PLP mRNA might regulate PLP RNA stability, C6 cells were transfected with cDNAs that expressed either luciferase or luciferase fused to the 3UTR of PLP. Although transgene expression was low, in cells transfected with the PLP 3UTR, there was a significant decrease in the endogenous PLP mRNA. These cells showed a distinct change in morphology and in adhesion properties. Thus, there may be a role for plp gene products in cell adhesion, which was downregulated in these cells, or an unknown function may be encoded by the PLP 3UTR. Transgenic mice that overexpress enhanced green fluorescent protein fused to the PLP 3UTR under control of PLP regulatory sequences were tested for the expression of the endogenous PLP mRNA. Three of four lines of transgenic mice had decreased endogenous PLP mRNA, relative to their non-transgenic littermates; the EGFP-PLP 3UTR mouse line that expressed the highest level of transgene mRNA had a 54% reduction in PLP mRNA. We hypothesize that the PLP mRNA is regulated by elements in the 3UTR and stabilizing proteins specific to oligodendrocytes, and that in cells that overexpress the PLP 3UTR, these stabilizing proteins may be insufficient to maintain the normal level of the endogenous PLP mRNA.     

Hydrophobic Regions in Myelin Proteins Characterized Through Analysis of "Hydropathic"Profiles

Computer-generated "hydropathic" profiles were constructed for graphic comparison of the amino acid sequences for P2 protein, 18.5 kilodalton (kDa) myelin basic protein (BP), and myelin proteolipid protein (PLP). Profiles were also obtained for cytochrome b5, a membrane protein known to be capable of reversible association with lipid bilayers and of a size comparable to that of the myelin BPs. Analysis of the PLP sequence produced profiles generally compatible with the suggestions that PLP has three transbilayer and two bilayer intercalating segments. Profiles for P2 and 18.5 kDa BP were found to contain hydrophilic segments separated by relatively short hydrophobic regions. Whereas hydropathic indices in hydrophobic regions of P2, 18.5 kDa BP, and PLP fall in the value ranges recently reported for cores of globular proteins and intrabilayer domains of membrane proteins, hydrophobic sections of P2 and 18.5 kDa BP have hydropathic indices similar to those in the hydrophobic core (transprotein) regions of globular proteins. None of them are comparable to the region of cytochrome b5 known to anchor that protein in its membrane or to the segments of PLP sequence proposed as intrabilayer domains. This comparison suggests that neither BP has structural characteristics compatible with insertion into the hydrocarbon core of the myelin lipid bilayer, a conclusion that is consistent with a recently published study that identified the bilayer penetrating proteins of myelin with a hydrophobic probe. The above findings suggest an enhancement for some details of myelin architecture and a cautious approach to interpreting data for BP intercalation into bilayers.     

Structural Analysis ofArabidopsis thaliana Chromosome 5. VI. Sequence Features of the Regions of 1,367,185 bp Covered by 19 Physically Assigned P1 and TAC Clones

Nineteen Pl and TAC clones, which have been mapped on the finephysical map of the Arabidopsis thaliana chromosome 5, weresequenced according to the shotgun-based strategy, and theirstructural features were analysed. The total length of the regionssequenced in this study was 1,367,185 bp. Combining this withthe regions covered by 90 P1 and TAC clones proviously reported,the total length of chromosome 5 sequenced to date becomes 8,058,855bp. On the basis of similarity search against protein and ESTdatabases and gene modeling with computer programs, a totalof 330 potential protein-coding regions were identified, bringingan average density of the genes to approximately one gene per4.1 kb. Introns were identified in 81.0% of the potential proteingenes for which the entire gene structure was predicted, withan average number per gene of 4.2 and an average length of theintrons of 180 bp. The RNA-coding genes identified were 9 tRNAgenes corresponding to 8 amino acid species and 2 genes forU2 nuclear RNA. These sequence features are essentially identicalto those in the previously reported sequences. The sequencedata and gene information are available on the World Wide Webdatabase KAOS (Kazusa Arabidopsis data Opening Site) at http://www.kazusa.or.jp/arabi/.     

Selection of mRNA 5'-untranslated region sequence with high translation efficiency through ribosome display

The 5′-untranslated region (5′-UTR) of mRNAs functions as a translation enhancer, promoting translation efficiency. Many in vitro translation systems exhibit a reduced efficiency in protein translation due to decreased translation initiation. The use of a 5′-UTR sequence with high translation efficiency greatly enhances protein production in these systems. In this study, we have developed an in vitro selection system that favors 5′-UTRs with high translation efficiency using a ribosome display technique. A 5′-UTR random library, comprised of 5′-UTRs tagged with a His-tag and Renilla luciferase (R-luc) fusion, were in vitro translated in rabbit reticulocytes. By limiting the translation period, only mRNAs with high translation efficiency were translated. During translation, mRNA, ribosome and translated R-luc with His-tag formed ternary complexes. They were collected with translated His-tag using Ni-particles. Extracted mRNA from ternary complex was amplified using RT-PCR and sequenced. Finally, 5′-UTR with high translation efficiency was obtained from random 5′-UTR library.     

Structural Analysis of Arabidopsis thaliana Chromosome 5. VII. Sequence Features of the Regions of 1,013,767 bp Covered by Sixteen Physically assigned P1 and TAC Clones

Sixteen Pl and TAC clones assigned to Arabidopsis thaliana chromosome5 were sequenced, and their sequence features were analyzedusing various computer programs. The total length of the sequencesdetermined was 1,013,767 bp. Together with the nucleotide sequencesof 109 clones previously reported, the regions of chromosome5 sequenced so far now total 9,072,622 bp, which presumablycovers approximately one-third of the chromosome. A similaritysearch against the reported gene sequences predicted the presenceof a total of 225 protein-coding genes and/or gene segmentsin the newly sequenced regions, indicating an average gene densityof one gene per 4.5 kb. Introns were identified in 72.4% ofthe potential protein genes for which the entire gene structurewas predicted, and the average number per gene and the averagelength of the introns were 3.3 and 163 bp, respectively. Thesesequence features are essentially identical to those in thepreviously reported sequences. The sequence data and gene informationare available on the World Wide Web database KAOS (Kazusa Arabidopsisdata Opening Site) at http://www.kazusa.or.jp/arabi/.     

植物转录抑制子的结构特征及其作用机理

转录因子依转录调控能力可分为激活子和抑制子。植物转录抑制蛋白的分类依据很多,从作用方式上可分为主动抑制子和被动抑制子两大类：根据与DNA结合的方式则可分为锌指类、MYB类、AP2／EREBP类、bHLH类和bZlP类等。植物主动抑制子通过其含有的抑制域对转录直接起抑制作用。抑制域又可分很多类,但多数为含有类似EAR基序的保守性基序,其上具有几个保守性亮氨酸残基。植物转录抑制子主要通过对激活子或基本转录复合物产生作用及改变染色体结构3种方式来抑制目标基因的转录。有关植物转录抑制子的研究虽很欠缺,但以拟南芥SUPERMAN等抑制子的EAR基序为代表的研究表明,抑制域是阐明植物转录抑制子功能和下游基因表达调控机理的核心对象,而融合抑制子沉默技术（CRES-T）也为人为调控基因沉默带来了新的技术手段。     

A 5'-terminal phosphate is required for stable ternary complex formation and translation of leaderless mRNA in Escherichia coli

The bacteriophage λ's cI mRNA was utilized to examine the importance of the 5'-terminal phosphate on expression of leadered and leaderless mRNA in Escherichia coli. A hammerhead ribozyme was used to produce leadered and leaderless mRNAs, in vivo and in vitro, that contain a 5'-hydroxyl. Although these mRNAs may not occur naturally in the bacterial cell, they allow for the study of the importance of the 5'-phosphorylation state in ribosome binding and translation of leadered and leaderless mRNAs. Analyses with mRNAs containing either a 5'-phosphate or a 5'-hydroxyl indicate that leaderless cI mRNA requires a 5'-phosphate for stable ribosome binding in vitro as well as expression in vivo. Ribosome-binding assays show that 30S subunits and 70S ribosomes do not bind as strongly to 5'-hydroxyl as they do to 5'-phosphate containing leaderless mRNA and the tRNA-dependent ternary complex is less stable. Additionally, filter-binding assays revealed that the 70S ternary complex formed with a leaderless mRNA containing a 5'-hydroxyl has a dissociation rate (k(off)) that is 4.5-fold higher compared with the complex formed with a 5'-phosphate leaderless mRNA. Fusion to a lacZ reporter gene revealed that leaderless cI mRNA expression with a 5'-hydroxyl was >100-fold lower than the equivalent mRNA with a 5'-phosphate. These data indicate that a 5'-phosphate is an important feature of leaderless mRNA for stable ribosome binding and expression.     

珍稀濒危植物独叶草的生物学特性及保护对策

对我国特有的珍稀濒危植物独叶草的生物学特性,包括其形态特征、生长特性、生境特点、群落学特性和地理分布进行了较系统的综述,分析了独叶草濒危的可能原因,并提出了一些保护措施.     

Evolution of green plants and their relationship with other photosynthetic eukaryotes as deduced from 5S ribosomal RNA sequences

The nucleotide sequence of cytoplasmic 5S ribosomal RNAs from three gymnosperms,Pinus contorta, Taxus baccata andJuniperus media and from one fern,Pteridium aquilinum, have been determined. These sequences were aligned with all hitherto known cytoplasmic 5S ribosomal RNA sequences of photosynthetic eukaryotes. A dendrogram based on that set of sequences was constructed by a distance matrix method and the resulting tree compared with established views concerning plant and algal evolution. The following monophyletic groups of photosynthetic eukaryotes are recognizable: theRhodophyta, a group consisting ofPhaeophyta, Bacillariophyta andChrysophyta, and the green plants, the latter comprising green algae,Bryophyta, Pteridophyta andSpermatophyta. According to our 5S ribosomal RNA tree, green plants may have originated from some type of a green flagellated organism such asChlamydomonas. The land plants seem to have originated from some form of charophyte such asNitella. 5S ribosomal RNA seems to be less appropriate to estimate dissimilarities between species which have diverged relatively recently, like the angiosperms. Therefore, a precise evolutionary process is difficult to reconstruct for members of this group.     

Regulation of Chitinase Production by the 5'-Untranslated Region of the ybfM in Serratia marcescens 2170

Glycine-rich protein (GRP), a cell wall protein, was extracted with hot water from the aleurone layer of soybean seeds. GRP was purified by adsorption on DEAE-Sephadex, Sephadex G-100 gel chromatography, and anion exchange HPLC. The estimated molecular size of GRP was approximately 30 kDa and GRP contained 59% glycine and 15% serine. The N-terminal amino acid sequence was a novel Gly-Gly-Gly-Gly-Gly-Gly-Gly-Gly-Gly-Gly-Gly-Gly-Gly-Gly-Gly-.     

庞泉沟自然保护区菊科植物药用功能分析

分析庞泉沟国家级自然保护区菊科植物药用功能.以吕梁学院馆藏植物标本为主线,通过实地查证与采集,对菊科药用植物的生物学特性、生境特点、药用部位及功效进行了归纳与分类.结果显示:庞泉沟自然保护区菊科药用植物资源有41种,隶属于25属;多为草本植物,其中以多年生草本植物最为丰富,一年生草本其次;药用部位较广泛,以全草类入药居...