CdCl2对质粒的生态效应及质粒在其宿主抗镉性中的作用

用CdCl₂处理体外或大肠杆菌体内质粒pWH58后,通过琼脂糖电泳和限制性内切酶分析,研究了Cd对质粒DNA结构的影响.通过比较带质粒与不带质粒大肠杆菌在含不同浓度CdCl₂的氨苄LB与无抗LB培养液中的生长量,研究了Cd对大肠杆菌体内质粒的影响及质粒在其宿主Cd耐性的作用.结果表明,体外、体内CdCl₂处理对质粒pWH58DNA结构无明显诱变性.Cd胁迫下大肠杆菌体内质粒pWH58可进行复制传代和基因表达.质粒pWH58降低了其宿主———大肠杆菌HB101的Cd耐性,使其宿主Cd耐性最高从75μg·ml^-1降至50μg·ml^-1.Cd驯化处理可提高大肠杆菌HB101的Cd耐性,但经修复培养后其Cd耐性趋于回复原有水平,表明大肠杆菌HB101的Cd耐性是可诱导的,但此诱导的Cd耐性尚无遗传基础.     

柯萨奇B3病毒结构和非结构蛋白基因重组质粒的构建及其在体外真核细胞中的

制备ＣＶＢ３结构蛋白和非结构蛋白重组质粒ＤＮＡ疫苗时,采用ＲＴ－ＰＣＲ从ＣＶＢ感染的ＨｅＬａ细胞中扩增ＶＰ１、ＶＰ２、２Ａ和３Ｄ基因,重组入真核表达质粒ｐｃＤＮＡ３中,构建ｐｃＤＮＡ３／ＶＰ２、ｐｃＤＮＡ３／ＶＰ１、ｐｃＤＮＡ３／２Ａ和ｐｃＤＮＡ３／３Ｄ重组质粒,经酶切和测下实扩增的序列并将各重组质粒体外转染真核细胞ＣＯＳ－７,用ＲＴ－ＰＣＲ检测ｍＲＮＡ的转录,用Ｗｅｓｔｅｒｎ－ｂｌｏｔ检测表达产物。结果４种重组质粒酶切出相应大小的目的片段,经测序证实为ＣＶＢ３相应序列,Ｗｅｓｔｅｒｎ－ｂｌｏｔ证实能够在体外真核细胞中表达。本文成功构建ＣＶＢ３结构与非结构蛋白的重组质粒ＤＮＡ疫苗,为进一步研究其免疫效果奠定了基础。     

肠聚集性大肠杆菌质粒的研究

本文介绍了肠聚集大肠杆菌（ＥＡｇｇＥＣ）质粒的同源性与质粒ＤＮＡ探针,质粒对粘附等特性的介导以及质粒ＤＮＡ的基因结构等的研究现状。     

转小鼠金属硫蛋白cDNA枸杞的获得及其检测

小鼠金属硫蛋白－ＩｃＤＮＡ通过根癌农杆菌介导转枸杞,枸杞体内的表达产物对重金属镉有一定的抗性。用带有嵌合ｍＭＴ－ＩｃＤＮＡ及Ｃａ ＭＶ３５ｓ启动子的含非致瘤性Ｔｉ持粒载体的根癌农杆菌ＬＢＡ４４０４感染枸杞幼茎外植体,在含有卡那霉素１００μｇ／ｍＬ和５０μｍｏｌ／Ｌ Ｃｄ＾２＋的选择培养基上筛选转化的愈伤组织,并在含卡那霉素５０μｇ／ｍＬ和１００μｍｏｌ／Ｌ,Ｃｄ＾２＋的分化培养基上得到再生小芽。     

Cd2+、Al3+对蚕豆(Vicia faba)DNA合成及修复的影响

利用＾３Ｈ－ＴｄＲ掺入方法,研究了不同浓度单金属离子Ｃｄ＾２＋、Ａｌ＾３＋对蚕豆ＤＮＡ合成、ＤＮＡ修复（以ＵＤＳ为指标）的影响。结果表明：在低浓度Ｃｄ＾２＾＋、Ａｌ＾３＋（Ｃｄ＾２＋浓度〈２００ｍｇ／ｌ,Ａｌ＾３＋浓度１００ｍｇ／ｌ）处理后,蚕豆ＤＮＡ合成加快,并且不同程度地诱导了ＵＤＳ的发生;但在高于此浓度的Ｃｄ＾２＋、Ａｌ＾３＋作用下,蚕豆ＤＮＡ合成受抑制,浓度越高,抑制作用超强;并且几乎不表     

BALB／C小鼠的白内障突变与大片段小卫星DNA多态性的变化

为了探讨ＢＡＬＢ／Ｃ小鼠白内障突变品系与ＢＡＬＢ／Ｃ小鼠保种品系二者间小卫星ＤＮＡ多态性的变化,为进一步研究变异小卫星位点与白内障突变基因的关系最终找到导致这种白内障形成的基因奠定基础,采用α－＾３２Ｐ－ｄＣＴＰ标记的人类小卫星ＤＮＡ探针Ｍｙｏ,通过Ｓｏｕｔｈｅｒｎ杂交比较了正常ＢＡＬＢ／Ｃ和ＢＡＬＢ／Ｃ白内障突变体小卫星ＤＮＡ多态性的变化。结果：ＢＡＬＢ／Ｃ白内障小鼠种内ＤＮＡ多态性带纹分布高度     

麦迪霉素4″—O—丙酰基转移酶（mpt）基因结构的研究

对含有麦迪霉素４″－Ｏ－丙酰基转移酶（ｍｐｔ）基因的ＢａｍＨＩ－ＢａｍＨＩ８．０ｋｂ的ＤＮＡ片段进行限制性酶切分析,绘制出了含有２１个酶切位点的限制性酶切图谱。以含有碳霉素异戊酰基转移酶基因（ＣａｒＥ）的２．４ｋｂ ＤＮＡ片段为探针,经Ｓｏｕｔｈｅｒｎ ｂｌｏｔ分子杂交,将ｍｐｔ定位于一个ＥｃｏＲＩ－ＥｃｏＲＩ－ＰｓｔＩ３．０ｋｂ的ＤＮＡ片段上,将该片段克隆至大肠杆菌／链霉菌穿梭质粒载体ｐＷＨＭ３     

PUC衍生质粒的一个低拷贝数突变型

本文报道大肠杆菌的ColE1类似质粒的一个低拷贝数突变型。从载体质粒pUC4衍生的重组质粒pPGVT3在大肠杆菌宿主DF2145中是不稳定的,以pPGVT3转化DF2145时在4o℃培养得不到转化子。用诱发点突变的羟胺体外处理pPGVF3质粒DNA,得到一个稳定性提高了的突变质粒pPGVT3HA,突变的位置被确定在质粒的pUC部分,突变降低了pUC及其衍生质粒的拷贝数。文中对质粒的稳定性与拷贝数的关系作了讨论。     

用多寄主质粒pSUP106转化荧光假单胞菌Pfx—18

构建了荧光假单胞菌工程菌的转化系统,探索了多寄主质粒ｐＳＵＰ １０６在不同ＣａＣｌ２浓度、不同热激时间和荧光假单胞菌受体在不同生长期的转化频率,建立了一个简便可行的荧光假单胞菌转化方法。结果表明,在荧光假单胞菌Ｐｆｘ－１８生长到０Ｄ６００≈０．５５时,用２５ｍｍｏｌ／Ｌ,ＣａＣｌ２处理细胞,热激２ｍｉｎ,转化频率最高,可达１０＆５／ｎｇ ＤＮＡ。同时讨论了Ｍｎ＾２＋和Ｍｇ＾２＋对转化频率的影响,以     

重组质粒转染蟑螂对黑胸大蠊浓核病毒的拯救

用Ｇｌａｓｓｍｉｌｋ法纯化ＰｆＤＮＶｄｓＤＮＡ,在其３′端和ＰｓｔⅠ切开的ｐＵＣ１１９质粒的３′端分别加ｄＧ和ｄＣ尾,连接、转化、筛选得到分子量为８．７ｋｂ的重组质粒。通过酶切证明插入ＤＮＡ为ＰｆＤＮＶ全基因组ＤＮＡ。利用ＤＥＡＥｄｅｘｔｒａｎ转染技术,将此重组质粒导入黑胸大蠊幼虫体内,此重组质粒能使虫体发病死亡。电镜超薄切片观察发现虫体细胞内存在大量的病毒粒子。同样,在免疫扩散实验中虫体ＰＢＳ浸出液能与抗ＰｆＤＮＶ的抗体产生沉淀线。用重组质粒感染致死的虫体喂食健康黑胸大蠊,也能使其发病死亡,通过电镜可以观察到在细胞内增殖的病毒粒子。     

Homologous recombination and mutagenesis of gamma-irradiated plasmid DNA in Escherichia coli host cells

Plasmid DNA was used to study gamma-radiation-induced recombination and mutagenesis in Escherichia coli host cells. Plasmid pBRP1, a derivative of pBR322 containing the lac operon of E. coli, was irradiated with 60Co gamma rays prior to transformation into E. coli strains of different recA and lac genotypes. Plasmid-chromosome recombination was assayed in lacY1 host cells, whereas plasmid mutagenesis was assayed in delta lac host cells lacking chromosomal sequences homologous to the plasmid. Both recombinant and mutant plasmids were identified by the phenotypic changes in lactose utilization, and confirmed by restriction analysis of isolated plasmids. Plasmid-chromosome recombination was induced to high levels (about 20% of survivors at 700 Gy) and was dependent on the host recA gene. Plasmid mutagenesis occurred at lower levels (about 1.5% of survivors at 600 Gy) and was relatively independent of the recA gene. Plasmid survival was unaffected by the presence or absence of host recA mutations or the potential for plasmid-chromosome recombination.     

Sensitivity of chromosomal and plasmid E. coli DNA to restriction endonuclease Eco RII]

It was shown that E. coli C, E. coli MRE 600 DNA, and also plasmid DNA of Col E1, RSF 2124 from E. coli K-12, and plasmid DNA from E. coli MRE 600 were completely resistant against restriction endonuclease R. Eco RII. Plasmid DNAs of Col E1, RSF 2124 amplificated for 4 hours in the presence of chloramphenicol are sensitive to R. Eco RII but after 16-hour amplification in the presence of chloramphenicol these DNAs acquire complete resistance against R. Eco RII. These data point to the slower rate of modification of DNA in vivo by DC-methylases of Eco RII type in comparison with DNA methylase Eco RII.     

A functional lagging strand origin does not stabilize plasmid pMV158 inheritance in Escherichia coli

Plasmid rolling circle replication generates single-stranded DNA intermediates. The intracellular amount of these molecules depends upon the efficiency of the conversion of single-stranded into double-stranded plasmid forms, that is, the functionality of the lagging strand origin (sso). The broad-host-range streptococcal plasmid pMV158 harbors two different ssos, both of which function efficiently in Streptococcus pneumoniae but poorly in Escherichia coli. Plasmid pMV158 is stably inherited in the pneumococcal host, but it is unstable in E. coli. A pMV158 derivative lacking its two ssos is unstable in both strains. We have cloned into this derivative the coliphage f1 lagging strand origin. Whereas the f1 sso was fully functional in E. coli, it did not show any activity in S. pneumoniae, a bacteria closely related to the pMV158 natural host. The presence of the f1 sso did not stabilize pMV158 inheritance in either the gram-positive or the gram-negative host.     

Relaxation of supercoiled plasmid DNA by oxidative stresses in Escherichia coli.

The relaxation of plasmid DNA was observed after the visible light irradiation of Escherichia coli AB1157 harboring plasmid pBR322 or some other plasmids in the presence of a photosensitizing dye, such as toluidine blue or acridine orange, and molecular oxygen. Treatment of the cells with hydroperoxides, such as tert-butyl hydroperoxide, cumene hydroperoxide, and hydrogen peroxide, also caused the plasmid DNA relaxation in vivo. Relaxation was not observed in these treatments of purified pBR322 DNA in vitro. Plasmid DNA relaxation was also detected after near-UV irradiation. Far-UV irradiation did not induce such relaxation.     

Transformation and expression of a staphylococcal plasmid in Escherichia coli

Abstract A multiple antibiotic-resistant Staphylococcus aureus , was found to possess three plasmid bands in agarose gel electrophoresis. A plasmid of approximately 4.3 kb (pMC790/2) was found to code for ampicillin and tetracycline resistance and to have one Eco RI site when transformed into S. aureus RN 4220. pMC790/2 in unmodified form was transformed into a recA⁻ E. coli at a frequency of 1.2×10⁴ transformants/μg of plasmid DNA. Plasmid (pMC790/2) replicated, maintained itself stably and expressed far better in the E. coli host than in S. aureus .     

Absence of pyrimidine insertase activity in E. coli extracts, using plasmid DNA containing apyrimidinic sites

Plasmid DNA, isolated from mutants of E. coli that are deficient in both uracil-DNA glycosylase and deoxyuridine triphosphatase, contains significant amounts of uracil. This can be removed in vitro by the action of uracil-DNA glycosylase, creating apyrimidinic sites. We have used depyrimidinated plasmid DNA isolated in this way to test the ability of E. coli extracts to preferentially incorporate labeled deoxythymidine triphosphate. No pyrimidine-insertase activity was found in extracts of bacteria that were deficient in exonuclease III. The question of the existence of such an activity in E. coli cells is discussed.     

Indole inhibition of ColE1 replication contributes to stable plasmid maintenance

In the absence of active partitioning, strict control of plasmid copy number is required to minimise the possibility of plasmid loss at bacterial cell division. An important cause of multicopy plasmid instability is the formation of plasmid dimers by recombination and their subsequent proliferation by over-replication in a process known as the dimer catastrophe. This leads to the formation of dimer-only cells in which plasmid copy number is substantially lower than in cells containing only monomers, and which have a greatly increased probability of plasmid loss at division. The accumulation of dimers triggers the synthesis of the regulatory small RNA, Rcd, which stimulates tryptophanase and increases the production of indole. This, in turn, inhibits Escherichia coli cell division. The Rcd checkpoint hypothesis proposes that delaying cell division allows time for the relatively slow conversion of plasmid dimers to monomers by Xer-cer site-specific recombination. In the present work we have re-evaluated this hypothesis and concluded that a cell division block is insufficient to prevent the dimer catastrophe. Plasmid replication must also be inhibited. In vivo experiments have shown that indole, when added exogenously to a broth culture of E. coli does indeed stop plasmid replication as well as cell division. We have also shown that indole inhibits the activity of DNA gyrase in vitro and propose that this is the mechanism by which plasmid replication is blocked. The simultaneous effects of upon growth, cell division and DNA replication in E. coli suggest that indole acts as a true cell cycle regulator.     

Effects of recombinant plasmid content on growth properties and cloned gene product formation in Escherichia coli

Plasmid-host cell interactions have been investigated experimentally using Escherichia coli HB101, plasmid RSF1050 which contains the origin of replication of pMB1, and four other closely related copy number mutant plasmids. Growth characteristics of these recombinant strains and beta-lactamase activity expressed from a plasmid gene were investigated in Luria broth (LB) and in minimal medium (M9) containing in some cases casamino acids or different concentrations of alpha-methylglucoside, a competitive inhibitor of glucose transport. Maximum specific growth rates in LB and minimal media were reduced for increasing plasmid content per cell. Plasmid copy number increased when specific growth rate was reduced by changing medium composition. Growth rates of high copy number strains were less sensitive to alpha-methylglucoside than lower copy number strains and the plasmidfree host. The overall efficiency of plasmid gene expression, measured as the ratio of beta-lactamase specific activity to plasmid content, decreased significantly with increasing plasmid content in LB medium.     

Characterization of broad host range cryptic plasmid pCR1 from Corynebacterium renale

Plasmid pCR1 is a cryptic plasmid harboured by Corynebacterium renale. It is the smallest corynebacterial plasmid known to date. Although its natural host is animal corynebacteria, it can replicate in several strains of soil corynebacteria. It can also replicate in Escherichia coli, in which it is stably maintained. The copy number of pCR1 in this host is higher than that of pUC19, with which it shows unidirectional incompatibility. It is also incompatible with pBK2, a plasmid bearing the common corynebacterial replicon pBL1. Its size is 1488bp, as revealed by DNA sequencing. A total of eight open reading frames (ORF) were detected in this plasmid, the largest of which codes for a putative Rep protein of predicted molecular mass of 21kDa. The plasmid pCR1 can be mobilized by the plasmid R6K from E. coli to other corynebacteria. Sequence analysis revealed the presence of an oriT homologous to that of R64. An E. coli plasmid pKL1 shows more than 90% identity with pCR1. Like many coryenbacterial plasmids, pCR1 also replicates by rolling circle mode.