极端嗜热古菌DNA修复核酸内切酶的研究进展

极端嗜热古菌由于生活在高温环境,其基因组DNA面临着严重的挑战,因此,它们如何维持其基因组稳定是本研究领域最为关注的科学问题之一。极端嗜热古菌具有与常温微生物相似的自发突变频率,暗示着它们比常温微生物具有更加有效的DNA修复体系进行修复高温所造成的基因组DNA损伤。目前,极端嗜热古菌DNA修复的分子机制尚不清楚。核酸内切酶在DNA修复途径中发挥着重要的作用。基因组序列显示极端嗜热古菌编码多种DNA修复核酸内切酶,但是其研究尚处于初期阶段。本文综述了极端嗜热古菌DNA修复核酸内切酶Nuc S、Endo V、Endo Q、XPF和Hjc的研究进展,并对今后的研究提出了展望。     

G-四链体核酸的生物学功能

G-四链体是由富含鸟嘌呤的DNA或RNA折叠形成的高级结构。可形成G-四链体的序列在人基因组中广泛分布,涉及DNA复制、端粒维持、基因表达与调控以及遗传不稳定性等过程。研究发现有些化学合成的G-四链体序列也具有生物活性,如核仁素的核酸适体AS1411具有抑制恶性肿瘤增殖活性。G-四链体的生物学功能研究对于恶性疾病的发病机理和靶向治疗,以及设计开发核酸类抗癌药物有重要意义。     

功能核酸概念的内涵与外延

对功能核酸概念的分析需要建立在对功能核酸研究的基础上,从内涵和外延两个方面来进行探析。从内涵来看,它是对具有特殊结构、执行特定生物功能的核酸分子的统称;从外延来看,它包括适体、核酸核酶、核糖开关、发光核酸、修饰核酸、功能核酸裁剪、核酸自组装、功能核酸纳米材料、核酸纳米酶、核酸药物、核酸补充剂以及DNA存储技术等。目前功能核酸已成功地应用于生物传感、生物成像、生物医学等诸多领域。对功能核酸这一概念进行了探讨,并尝试对其范畴、特点进行归纳总结,以期梳理和完善功能核酸的基本概念,促进该领域的进一步发展。     

过氧化物酶体的稳态维持机制与膜接触位点

过氧化物酶体是保守存在于真核生物中的一种细胞器,参与多种生化代谢过程,包括脂肪酸β氧化反应、活性氧的产生和降解等。过氧化物酶体在生物发生和应对环境胁迫过程中,通过数量和时空分布的规律性动态变化,实现质量控制,以维持其生化代谢的稳态,从而保持机体的正常生命活动。同时,作为真核细胞的代谢枢纽,过氧化物酶体功能的正常发挥与稳态维持需要与其他细胞器相互协作。过氧化物酶体膜接触位点在过氧化物酶体与各细胞器相互连接和交流中发挥着重要作用。近年来,过氧化物酶体稳态维持机制和膜接触位点的组成和功能成为国内外相关研究的热点,本文对相关研究的进展进行了综述。     

亚甲基四氢叶酸还原酶(C677/T)基因的单核苷酸多态性

亚甲基四氢叶酸还原酶(methylene tetrahydrofolatucte redase,MTHFR)是叶酸代谢过程中的关键酶,对叶酸和同型半胱氨酸的代谢以及DNA的合成、修复与甲基化均有重要作用。MTHFR基因变异导致酶热稳定性及活性降低,引起相关代谢及DNA甲基化异常,进而发生相关疾病。MTHFR具有多种变异型,本文对其中常见的一种C677T的多态性及其与疾病的相关性的研究进展做一综述。     

核酸切割酶在病原微生物检测中的研究进展

DNA是遗传信息的重要载体,其空间构象折叠性质使其具有很多的功能。利用核酸切割酶(cleaving DNAzyme)识别特定单链DNA分子并能够切割其中某条单链的性质来构建传感器,将特异性识别过程转化为凝胶电泳表征、释放荧光、比色现象的信号输出,同时能很好的和扩增反应结合来实现信号放大。核酸切割酶通过体外筛选技术获得,可以与靶物质(小分子、蛋白质,甚至整个细胞)特异性结合。由于具有制备简单,易于修饰和良好稳定性等优点,核酸切割酶被用于构建生物传感器以检测病原微生物,已应用到现场检测甚至医疗中的体内检测,结合已经成熟的检测设备血糖仪、横流层析试纸条带进行微生物检测,并广泛地应用到生物传感、食品安全、医疗在内的重要领域中。综述了近年来核酸切割酶在微生物检测中的应用,讨论了核酸切割酶在微生物检测中的切割机理和产物、靶标以及表征手段,探索核酸切割酶在微生物实际检测中的意义。对该技术的发展前景及其面临的问题进行展望,以期核酸切割酶在微生物检测领域能够更好的发展。     

分子生物学手段在植物系统与进化研究中的应用

在植物系统与进化研究中,为了揭示真实本质,必须从分子水平进行研究。植物分子系统学的研究包括两大方面,一是蛋白质与酶,二是核酸。酶电泳是分子水平上研究植物分子遗传学最经济有效的方法,可以有效地揭示自然居群中遗传结构、基因流动、变化系统、选择作用和系统发育等问题。植物核酸系统学的研究倍受青睐,因为核酸分子是最基本的进化单元,几乎不受主观因素影响。相关的核酸分析技术主要有：DNA杂交、DNA限制酶谱分析、RFLP分析、DNA指纹图技术、RAPD分析和核酸序列分析。在植物系统学和进化研究中,结合各方面的生物学证据,才能显示植物分子系统学的独特优势。     

小议核酸合成的抑制物与防癌

当今,许多种病毒性疾病如乙肝、丙肝及肿瘤等严重威胁着人们的健康,然而对这些疾病还缺乏有效而可靠的治疗药物和防治方法。近年来为寻找选择性抑制病毒的药物,对病毒的复制规律及其宿主核酸代谢的差异发现,某些核酸代谢的桔抗物的抗菌素能与核酸或核酸合成有关的酶结合,从而抑制核酸的合成。其中有些可作为抗病毒和抗肿瘤药物,而在临床上得到广泛应用,对病毒和癌细胞化疗的研究有着重要的启示,也给患者带来了极大的希望。根据核酸合成的抑制物的结构和作用不同,可分为以下几类：（1）碱基类似物碱基类似物在体内作用主要有两方面…     

CRISPR技术在生物传感中的应用——胞内核酸成像、体外核酸检测与胞内DNA记录

核酸分子是生命的遗传物质和生命信息载体。如何观察细胞内外特定核酸序列,快速检测核酸序列和记录检测的细胞活动过程?这些在分子生物学领域重要的科学问题需要强有力的技术来解决。如今,在基因组编辑领域赫赫有名的CRISPR技术开始涉足上述领域。重点介绍CRISPR相关蛋白在生物传感方面的应用,包括细胞内特定基因组序列和RNA的成像、体外核酸快速检测以及细胞内DNA记录。核酸成像与核酸检测是将特定核酸序列的信息,通过CRISPR蛋白的参与转化为易检测的信号(如荧光);而DNA记录则是将细胞的代际或所接触的信号转化为细胞内DNA序列进行储存。这些新兴研究方向的开发和发展将大大促进CRISPR技术在基础科学、合成生物学、分子诊断等领域的应用。     

末端脱氧核苷酸转移酶在生物传感及核酸合成领域的应用*

末端脱氧核苷酸转移酶(terminal deoxynucleotidyl transferase, TdT)是聚合酶X家族中的一员,与典型的DNA聚合酶不同,TdT以恒温的无模板依赖的方式催化脱氧核糖核苷三磷酸(dNTP)聚合到寡核苷酸的3'羟基端来合成DNA。并且TdT对底物的耐受性高具有聚合修饰型dNTP的能力,如荧光修饰的dNTP、生物素修饰的dNTP,甚至人工碱基均可作为其良好底物。TdT的这些生化特性使其被广泛的应用在生物传感和核酸合成领域中,促进了许多基于核酸的工具和方法的发展,并为酶促从头合成DNA技术的发展奠定基础。介绍了TdT的性质,重点总结了它在其介导的生物检测技术、核酸的修饰技术以及酶促合成DNA技术三个方面的核心作用、目前面临的挑战以及未来研究的方向,以期促进TdT在生物传感器和核酸合成中的进一步应用。     

A Unique Protease Cleavage Site Predicted in the Spike Protein of the Novel Pneumonia Coronavirus (2019-nCoV) Potentially Related to Viral Transmissibility

正Dear Editor,In December 2019, a novel human coronavirus caused an epidemic of severe pneumonia(Coronavirus Disease 2019,COVID-19) in Wuhan, Hubei, China(Wu et al. 2020; Zhu et al. 2020). So far, this virus has spread to all areas of China and even to other countries. The epidemic has caused 67,102 confirmed infections with 1526 fatal cases     

Curcuminoids as inhibitors of thioredoxin reductase: A receptor based pharmacophore study with distance mapping of the active site

Curcumin is the yellow pigment of turmeric that interacts irreversibly forming an adduct with thioredoxin reductase (TrxR), an enzyme responsible for redox control of cell and defence against oxidative stress. Docking at both the active sites of TrxR was performed to compare the potency of three naturally occurring curcuminoids, namely curcumin, demethoxy curcumin and bis-demethoxy curcumin. Results show that active sites of TrxR occur at the junction of E and F chains. Volume and area of both cavities is predicted. It has been concluded by distance mapping of the most active conformations that Se atom of catalytic residue SeCYS498, is at a distance of 3.56 from C13 of demethoxy curcumin at the E chain active site, whereas C13 carbon atom forms adduct with Se atom of SeCys 498. We report that at least one methoxy group in curcuminoids is necessary for interation with catalytic residues of thioredoxin. Pharmacophore of both active sites of the TrxR receptor for curcumin and demethoxy curcumin molecules has been drawn and proposed for design and synthesis of most probable potent antiproliferative synthetic drugs.     

Comparative morphology of the carpel in the Liliaceae: Hewardieae, Petrosavieae, and Tricyrteae

The young pistils in the melanthioid tribes, Hewardieae, Petrosavieae and Tricyrteae, are uniformly tricarpellate and syncarpous. They lack raphide idioblasts. All are multiovulate, with bitegmic ovules. The Petrosavieae are marked by the presence of septal glands and incomplete syncarpy. Tepals and stamens adhere to the ovary in the Hewardieae and the Petrosavieae but not in the Tricyrteae. Two vascular bundles occur in the stamens of the Hewartlieae and Tricyrtis latifolia. Ventral bundles in the upper part of the ovary of the Hewardieae are continuous with compound septal bundles and placental bundles in the lower part. Putative ventral bundles occur in the alternate position in the Tricyrteae and putative placental bundles in the opposite. position in the Petrosavieae. The dichtomously branched stigma in each carpel of the Tricyrteae is supplied by a bifurcated dorsal bundle.     

Selection with two alleles and complete dominance

For a plant selection model with frequency-independent viabilities, fertilities and selfing rates, it is shown that apart from global fixation, for certain parameter combinations a protected polymorphism and facultative fixation (either allele may become fixed according to initial frequencies) may both occur. Facultative fixation requires different selling rates for the dominant and recessive type. Protection of the polymorphism requires resource allocation for male and female function. In this connection the problem of purely genetically caused population extinction is discussed.
For general frequency dependence and regular segregation, the chances for establishment of a completely recessive gene are compared to those of a completely dominant gene. It is proven that the process of establishment of the recessive gene, despite a fitness advantage, may be considerably endangered by drift effects if random mating prevails. The recessive gene may reach the same effectivity in establishment as a dominant gene, only if the recessive homozygote mates exclusively with its own type during the period of establishment.     

Composition and diversity of bird communities in Swedish farmland–forest mosaic landscapes

CapsuleThe amount of forest (at local and landscape scales) and occurrence of residual habitats at the local scale are shown to be the major factors influencing bird community composition in farmland–forest landscapes in central Sweden.

Aims To investigate the importance of local habitat and landscape structure for breeding birds in farmland–forest landscapes in central Sweden.

Methods Breeding birds were censused at 292 points. A detailed habitat mapping was made within 300 m of the points. Within a 300–600 m radius only two major habitats (forests and arable fields) were identified.

Results Cluster analyses of bird communities identified three site types that also differed in habitat composition: (i) partially forested sites in forested landscapes; (ii) heterogeneous sites with residual habitats in mosaic landscapes; and (iii) field-dominated farmland sites in open landscapes. A total of 19 of 25 farmland bird species (restricted to farmland or using both farmland and forest) had the highest abundance in farmland sites with mosaics of forest and farmland, while only six farmland species had the highest abundance in field-dominated sites. The bird community changed from being dominated by farmland species to being dominated by forest species (common in forest landscapes without farmland) at small proportions (10–20%) of forest at the local scale. A major difference in habitat composition between heterogeneous and field-dominated sites was the occurrence of different residual habitats (e.g. shrubby areas and seminatural grasslands). These habitats seemed to influence bird community composition more than land-use, despite covering <10% of the area. Seminatural grasslands were important for bird community composition and species-richness, but grazing seemed to be less important. Among different land-use types, cereal crops were the least preferred fields. Set-asides with tall vegetation and short rotation coppices were positively associated with species-richness of farmland birds.

Conclusion In general, the composition of the landscape was important for bird community composition, although amount and distribution of forests, occurrence of residual habitats and land-use of fields at the local scale had the strongest influence on bird community composition. The possible implications of these patterns for managing farmland–forest landscapes are discussed.     

Chemical constituents from the fruits of Rhus typhina L. and their chemotaxonomic significance

This work describes the isolation and characterization of twenty-nine compounds from the fruits of Rhus typhina L., including eleven flavonoids (1–11), eleven phenols (12–22), two pentacyclic triterpenes (23–24), two organic acids (25–26), one lumichrome (27), one courmarin (28) and one pyrimidine (29) on the basis of their spectroscopic data. Compounds apigenin (1), daidzein (4), orobol (5), 3′, 5, 5′, 7-tetrahydroxyflavanone (6), naringenin (7), butein (8), (-)-catechin (9), quercetin-3-O-α-L-(3″-O-galloyl)-rhamnoside (11), 2-hydroxybenzoic acid (13), 4-hydroxybenzaldehyde (14), vanillin (15), methyl 3,4-dihydroxybenzoate (16), 3,5-dihydroxybenzamide (18), tyrosol (19), caffeic acid (20), 3-(2,4,6-trihydroxyphenyl)-1-(4-hydroxyphenyl)-propan-1-one (21), phlorizin (22), friedelin (23), oleanolic acid (24), 4,4-dimethyl-heptanedioic acid (25), anthranilic acid (26), lumichrome (27), scoparone (28) and uracil (29) have not been recorded before in this plant. This is the first report on the occurrence of compounds 4–7, 9, 11, 13–14, 16, 18–21, 25–29 from the genus Rhus. Moreover, the chemotaxonomic significance of these isolated compounds was also summarized.