动物的的变态

变态是动物学中一个较重要的专用名词,有关内容在中学课本也多处涉及到。现择要介绍一点动物变态的知识,供动物学教学参考。何谓动物的变态动物由于外在和内在的原因,个体形态发生变化,这叫变态。但动物学所讲的变态,是狭义地从发生学角度理解,即胚胎不直接转变为成体,而是在后期发育过程中,先形成形态、生理、生态方面特殊的幼体,行独立生活和生长,以后在某阶段发生急剧变化,转变为成体。青     

活的不可培养的细菌的研究进展

活的不可培养微生物(VBNC)即一些微生物明显地丧失了可培养的特性,但是保留了自身原有的代谢活力,并且在一定条件下,又可以回复到可培养的状态。从VBNC细菌的诱导条件、生物学特性和检测方法3个方面对VBNC细菌研究进展做一综述。     

真核细胞的基因的组织

一、真核细胞基因的基本结构 1.转录单位: 从已知的数十种基因的顺序,可得出一个具有功能的基因的共同规律,在基因5’端-25至-75区,有CCAAT和TATAAA区(后者又称ATA box或Hogness box),相当于促进子区(Promotor),为体外转录所必需。     

高频率的波动对于种子的萌发和植物的发育的影响

本文主要是以理论和试验来说明音波对植物的生长发育和种子萌发所起的影响。在农业实践上音波所起的作用,据现在所知:有缩短植物成熟期,加速萌芽和增强植物的生长发育等。这一些非但具有理论和实践上的意义,同时在今後把物理科学应用到农业科学中开辟了极广阔的前程。     

由吸附的缩氨酸诱导的细胞膜的形变

研究了由一系列相互平行的吸附在细胞膜上的缩氨酸引起的膜的弹性形变,以及膜对缩氨酸的包裹行为,得到膜的平衡方程,用它可以来处理大尺度的形变,弯曲能量、吸附能量和弹性形变的相互竞争导致膜对缩氨酸发生从不吸附到部分吸附乃至完全包裹的结构转变．在膜的形变很小的时候,可以得到系统能量的解析解。     

远古的人们是怎样认识自己的起源的

人是从那里来的? 回答这个问题,你也许会说这有什么困难——人是从古猿变来的;甚至你还会进一步说,在这个从猿到人的转变过程中,劳动起着决定性的作用。然而这个现在看来比较明了的道理,恰是经历了多么漫长的认识过程才达到的呵!现在让我们首先来谈谈,远古的人们是怎样认识自己的起源的。最初的原始人可能还想不到自己的起源在人类诞生的最早时期,“最初的、从动物界分离出来的人,在一切本质方面是和动物本身一样不自由的”(恩格斯:《反杜林论》),这些最初的原始人为艰苦     

敲除pckA基因的结核杆菌引起的免疫反应的研究

研究结核杆菌pckA基因编码的磷酸烯醇型丙酮酸羧激酶(PEPCK)诱导机体产生的保护性免疫反应。用敲除pckA基因的牛结核杆菌BCG和野生型BCG分别感染小鼠,取肝、肺、脾进行病理分析,并进行脾细胞培养,检测CD4 、CD4 /CD8 、细胞因子IFNI-γI、L-12和TNF等。用敲除pckA基因的BCG感染的小鼠比野生型BCG感染的小鼠体内产生的结核结节少且不典型,炎性程度低。野生型BCG感染的小鼠脾脏内的CD4 T细胞和CD4 /CD8 、细胞因子IFN-γ、IL-12、TNF均明显高于敲除pckA基因BCG感染的小鼠。pckA基因为结核杆菌生长所必需,其编码产物PEPCK能够刺激机体产生免疫反应,是一种很好的疫苗候选分子。     

分离的蚕豆细胞核的RNA聚合酶活力的研究

利用Triton X-100对叶绿体膜的作用,可快速地从蚕豆幼叶制备较纯净的细胞核,它具有较高的RNA聚合酶活力。比较了两种分离核的方法,证明利用匀浆法制备的核具有较高的活力。核活力与发育时期有关系,茎端和第1对幼叶的核活力显著高于第2和第3对叶片的核活力。此外,核活力明显地受反应液内锰离子的抑制。     

病毒来源的microRNA的研究进展

微小RNA(microRNA,miRNA/miR)是一类长度约为18～22个核苷酸的小非编码单链RNA,能够参与机体发育、细胞增殖、分化和肿瘤发生等一系列生物过程。病毒与宿主细胞一样,也可以编码miRNA,并在病毒感染过程中发挥重要的作用。本文从病毒编码miRNA的发现,经典与非经典的生物合成途径,以及病毒编码miRNA对宿主细胞和病毒自身作用机制等方面进行概述,以期为研究病毒来源的miRNA的生物学功能提供一定参考。     

一种简易的利用Pfu-DNA聚合酶进行反向长距离PCR获得定点突变的方法(英文)

定点突变是一种常用的分子生物学方法。利用Pfu_DNA聚合酶进行反向长距离PCR可以有效地获得定点突变。方法操作简易 ,突变效率高于 90 %。整个操作过程可在一个试管中完成 ,不需亚克隆。对克隆在大质粒 (如转化植物的Ti_类型质粒 )尤为实用。     

Stability of DNA triplexes on shuttle vector plasmids in the replication pool in mammalian cells

Triple helix-forming oligonucleotides may be useful as gene-targeting reagents in vivo, for applications such as gene knockout. One important property of these complexes is their often remarkable stability, as demonstrated in solution and in cells following transfection. Although encouraging, these measurements do not necessarily report triplex stability in cellular compartments that support DNA functions such as replication and mutagenesis. We have devised a shuttle vector plasmid assay that reports the stability of triplexes on DNA that undergoes replication and mutagenesis. The assay is based on plasmids with novel variant supF tRNA genes containing embedded sequences for triplex formation and psoralen cross-linking. Triple helix-forming oligonucleotides were linked to psoralen and used to form triplexes on the plasmids. At various times after introduction into cells, the psoralen was activated by exposure to long wave ultraviolet light (UVA). After time for replication and mutagenesis, progeny plasmids were recovered and the frequency of plasmids with mutations in the supF gene determined. Site-specific mutagenesis by psoralen cross-links was dependent on precise placement of the psoralen by the triple helix-forming oligonucleotide at the time of UVA treatment. The results indicated that both pyrimidine and purine motif triplexes were much less stable on replicated DNA than on DNA in vitro or in total transfected DNA. Incubation of cells with amidoanthraquinone-based triplex stabilizing compounds enhanced the stability of the pyrimidine triplex.     

Parallel assembly for multiple site-directed mutagenesis of plasmids

A parallel assembly method for multiple site-directed mutagenesis of plasmids was developed here based on Golden Gate cloning. It takes advantage of type IIs restriction enzymes and T4 DNA ligase to assemble multiple DNA fragments into a plasmid by a defined order. This method can accommodate multiple plasmid mutagenesis at any desired position with all three sequence modification types (substitution, deletion, and insertion) simultaneously. Furthermore, it can be used to create otherwise difficult-to-make mutants-larger deletions and insertions and mutagenesis on larger plasmids. The processes of mutagenesis can be completed quickly by a single restriction-ligation reaction.     

Rapid physical mapping by transposon Tn5 mutagenesis to localize the cloned yeast ILV2 gene

A rapid method for Tn5 mutagenesis of cloned genes on multicopy plasmids was used to map a yeast ILV2 mutant allele encoding a sulfometuron methyl-resistant acetolactate synthase. Twenty-one of 40 independent Tn5 insertions were within the 5.6-kilobase-pair cloned segment. Of these, seven adjacent transposition events inactivated the sulfometuron methyl resistance determinant, localizing the ILV2 gene to a minimum 1.4-kilobase-pair region.     

Plasmid-mediated expression of the UmuDC mutagenesis proteins in an Escherichia coli strain engineered for human cytochrome P450 1A2-catalyzed activation of aromatic amines.

The mutagenic actions of many chemicals depend on the activities of bacterial "mutagenesis proteins", which allow replicative bypass of DNA lesions. Genes encoding these proteins occur on bacterial chromosomes and plasmids, often in the form of an operon (such as umuDC or mucAB) encoding two proteins. Many bacterial strains used in mutagenicity testing carry mutagenesis protein genes borne on plasmids, such as pKM101. Our objective was to introduce mutagenesis protein function into Escherichia coli strain DJ4309. This strain expresses recombinant human cytochrome P450 1A2 and NADPH-P450 reductase and carries out the metabolic conversion of aromatic and heterocyclic amines into DNA-reactive mutagens. We discovered that many mutagenesis-protein plasmids severely inhibit the response of strain DJ4309 to 2-amino-3,4-dimethylimid-azo[4,5-f]quinoline (MeIQ), a typical heterocyclic amine mutagen. Among many plasmids examined, one, pGY8294, a pSC101 derivative carrying the umuDC operon, did not inhibit MeIQ mutagenesis. Strain DJ4309 pGY8294 expresses active mutagenesis proteins, as shown by its response to mutagens such as 1-nitropyrene and 4-nitroquinoline 1-oxide (4-NQO), and is as sensitive as the parent strain DJ4309 to P450-dependent mutagens, such as MeIQ and 1-aminopyrene.     

QuikChange shuffling: a convenient and robust method for site-directed mutagenesis and random recombination of homologous genes

Here we describe a robust method, termed QuikChange shuffling, for efficient site-directed mutagenesis and random recombination of homologous genes. The homologous genes are fragmented, and the random fragments are reassembled in a self-priming polymerase reaction to obtain chimeric genes. The product is then mixed with linearized vector and two pairs of complementary mutagenic primers, followed by assembly of the chimeric genes and linearized vector through QuikChange-like amplification to introduce recombinant plasmids with a site-directed mutation. The method, which can yield 100% chimeric genes after library construction, is more convenient and efficient than current DNA shuffling methods.     

Genetic analysis of an Agrobacterium tumefaciens strain producing an agrocin active against biotype 3 pathogens

Summary The successful biocontrol agent for crown gall disease, Agrobacterium radiobacter strain K84, is unable to protect grapevines from infection. We have identified a strain of Agrobacterium tumefaciens, J73, which produces an agrocin active both in vitro and in vivo against grapevine pathogens (Webster et al. 1986). We now report on the curing of this strain of its nopaline-type Ti plasmid and the location, by transposon mutagenesis, of the genes involved in the production of the agrocin. The Ti plasmid was cured by the introduction of selectable plasmids carrying the origins of replication of either the nopaline Ti plasmid, pTiC58, or the octopine Ti plasmid, pTi15955. Tn5 mutagenesis indicated that the genes responsible for agrocin production and/or export are located both on the chromosome and on a plasmid, pAgJ73, which co-migrated in agarose gels with pTiJ73. As the two plasmids were separable after transposon mutagenesis, we postulate that during or after mutagenesis of the agrocin plasmid, DNA rearrangements occurred between it and pTiJ73, resulting in an increase in size of pAgJ73. We provide evidence that the rearrangements involved the duplication of nopaline catabolism genes from pTiJ73 and their insertion into pAgJ73, which facilitated the resolution of the two plasmids. As expected pTiJ73 has homology with the nopaline Ti plasmid, pTiC58.