细菌染色体第1类整合子捕获耐药性基因盒反应模型的构建

【背景】整合子在细菌耐药性的获得及传播中占据重要地位,对于整合反应检测方法的改良及反应机制的研究,可以加深我们对细菌耐药性产生和播散的理解,为遏制耐药菌株的产生和播散提供新的途径。【目的】在细菌染色体上构建第1类整合子反应模型,用于评价整合酶介导的基因盒位点特异性重组。【方法】 PCR分别扩增含氯霉素耐药基因cat的CM片段、含基因盒aadA5的LacA5片段、含整合子重组位点attI1及强可变区启动子的PcS片段和插入位点两侧的同源臂,重叠延伸聚合酶链反应连接上述5个片段制备整合子模型插入片段,通过同源重组将构建好的整合子模型片段插入大肠埃希菌JM109染色体中。转入高表达第1类整合酶的质粒pHSint,在链霉素平板上筛选发生整合的菌株,并经聚合酶链反应和测序验证。【结果】构建的整合子模型片段经测序与预期一致,整合子模型片段成功插入大肠埃希菌JM109染色体中。转入高表达整合酶的质粒pHSint后,在链霉素平板上成功筛选出基因盒aadA5发生整合的菌株,经聚合酶链反应扩增并测序与预期一致。【结论】在大肠埃希菌染色体上成功构建第1类整合酶介导基因盒位点特异性重组反应模型,为进一步揭示整合子捕获耐药性基因盒的反应机制奠定基础。     

细菌整合子与移动性基因盒的研究进展

整合子是由整合酶基因、基因盒和基因盒附着位点三者组成的遗传元件.在整合酶介导下,整合子通过位点特异的重组系统获取并交换外源DNA(基因盒),即将基因盒整合到整合子上或将之从整合子上剪切下来,但是整合子本身不能够移动.本文综述了国外近年来关于整合子与基因盒的结构特征及其分类的研究近况,对了解整合子及与之密切相关的移动性基因盒在细菌的多重耐药和毒力研究中,尤其是在适应选择性压力下细菌基因组进化中的作用具有重要的意义.     

XerCD/dif位点特异性重组

大约10%~15%的大肠杆菌在染色体复制过程中会形成染色体二聚体。大肠杆菌染色体编码的重组酶XerC和XerD作用于染色体复制终点区的dif序列,以同源重组的方式将染色体二聚体解离为单体,使细菌得以正常复制分裂。编码霍乱毒素的噬菌体CTXΦ以位点特异的方式整合入霍乱弧菌染色体,但其基因组中不含有任何重组酶基因,其整合过程需要细菌染色体编码的XerC和XerD重组酶,且整合位点与大肠杆菌dif序列相似。XerCD重组酶基因和dif位点在细菌染色体广泛存在,表明其可能是染色体二聚体解离,噬菌体及其他外源基因成分整合入染色体过程中一种广泛存在的途径。文章对XerCD/dif位点特异性重组在细菌染色体二聚体解离、外源基因整合的研究进展进行综述。     

整合子与细菌耐药性的相关研究进展

整合子是广泛存在于细菌中的一种可移动基因元件,它可以捕获外来基因盒并使其在细菌体内得到表达,在细菌耐药性的传播过程中扮演着重要角色。过去研究认为,细菌耐药是在质粒及转座子~([1])等基因水平上广泛传播,近几年大量研究表明,细菌可通过位点特异性重组的方式将耐药基因盒捕获并整合到自身的染色体或者质粒DNA上,即细菌体内存在一种天然的基因克隆表达系统——整合子。细菌耐药的高频次出现已成为临床医疗工作中的瓶颈,整合子不仅在细菌耐药中起关键作用,而且在细菌适应性及基因进化中具有普遍又重要的意义。     

pEASY-E1-Int1表达载体的点突变改造与整合酶的表达分析

整合子—基因盒系统(Integron-gene cassette system)能使耐药基因在细菌种内和种间快速传播。在整合子—基因盒系统中起关键作用的是整合酶,本研究的目的在于克隆与NCBI公布的整合酶DNA序列完全一致的序列,并进一步表达纯化整合酶。采用PCR技术点突变改造pEASY-E1-Int1表达载体上的目的基因整合酶基因,共含5个突变位点,测序比对后,再连接与pEASY-E1 expression表达载体上,转化到BL21(DE3)感受态细胞中,不同浓度IPTG诱导优化表达,经聚丙烯酰氨凝胶电泳(SDS-PAGE)和Western blotting检测分析,结果得到表达产物分子量为33 kD与Ⅰ类整合子整合酶分子量一致的整合酶。本研究为下一步比较野生型和耐药性大肠杆菌整合酶活性提供基础指导。     

临床分离肺炎克雷伯菌Ⅰ类整合子的结构与功能

为了探索细菌多重耐药性的产生和播散的分子机制, 文章对2002～2007年间179株临床分离的肺炎克雷伯菌进行耐药性、I类整合子可变区基因盒结构以及基因盒携带的耐药性基因进行分段克隆和耐药性功能测定。结果显示：65.9%(118/179)的肺炎克雷伯菌表现出对至少两种以上的抗生素(主要为β-内酰胺类、氨基糖苷类和喹诺酮类抗菌药物)的耐药性; 36.3%(65/179)的菌株检出单条或者双条I类整合子基因盒条带; 对整合子阳性组与阴性组的耐药率进行比较发现, 除氨基糖苷类、喹诺酮类和复方新诺明等药物的耐药性存在显著性差异(P<0.01)外, 其余药物的差异不显著; 共发现15种耐药基因构成形式的整合子基因盒, 其中以dfrA17-aadA5最为多见, 实验证明整合子可由接合转移耐药性质粒携带; 对整合子基因盒(dhfr17-orfF-aadA2)分段克隆的耐药性功能研究发现, 3个克隆重组子(pET28a-dhfr17、pET28a-dhfr17-orfF和pET28a-dhfr17-orfF-aadA2)对复方新诺明的抗性(MIC值)均为256 µg/mL, 重组子pET28a-dhfr17-orfF与重组子pET28a-dhfr17对链霉素的抗性无明显区别, 和受体菌一样MIC值均为8 µg/mL, 而pET28a-dhfr17-orfF-aadA2对链霉素的抗性则明显提高, MIC值为256 µg/mL。结果表明, I类整合子在肺炎克雷伯菌中较常见, 携带氨基糖苷类和甲氧苄啶类的耐药基因盒在数量上占优势, 且整合子携带的耐药基因具有耐药性功能, 位于可水平转移耐药性质粒的耐药性基因相关的整合子对病原菌耐药性播散具有重要意义。 目的基因     

产超广谱β-内酰胺酶细菌中I类整合子的研究进展

产超广谱β-内酰胺酶(Extended-spectrum beta-lactamase, ESBLs)细菌的多重耐药性是临床用药的一大难题, 近年研究发现其耐药性的产生与整合子密切相关, 其中临床最常见、研究最深入的是I类整合子。整合子是一种可移动基因元件, 在整合酶的作用下捕捉外源基因盒并使之表达, 是具有基因整合和切除功能的天然克隆和表达系统。研究表明I类整合子可连续捕捉和整合多种耐药基因, 以质粒或转座子为载体在细菌之间传播耐药性, 使ESBLs细菌多重耐药趋势十分严峻。本文就I类整合子的结构特征、I类整合子对耐药基因盒的整合作用及其与ESBLs细菌耐药性的关系等方面进行综述。     

酿酒酵母位点特异性DNA切离及定点整合的研究

酿酒酵母２μ环的ＦＬＰ－ＦＲＴ位点特异性重组系统由ＦＬＰ重组酶和ＦＲＴ重组位点所组成。将ＦＬＰ基因置于受半乳糖调控的酵母ＧＡＬ１０启动子控制下,在半乳糖诱导下实现了酿酒酵母染色体上两个顺向排列ＦＲＴ位点之间ＤＮＡ序列的切离;并将一个含有ＦＲＴ重组位点的环状质粒整合到酿酒酵母染色体上预先设置的一个ＦＲＴ重组位点上,实现了染色体定点整合。这个由ＦＬＰ重组酶催化的位点特异性重组过程具有重组效率高和重组位     

卵母细胞特异表达ФC31整合酶载体pZP3－INT的构建及其在小鼠卵母细胞中的表达

链霉菌噬菌体ФC31整合酶是一种位点特异性重组酶（Site—specific recombinase,SSR）,可介导链霉菌噬菌体attP位点（Phage attachment site）和链霉菌基因组attB位点（Bacterial attachment site）闻的单向重组。为探讨它能否应用于卵母细胞特定基因的重组,文章采用卵巢针刺取卵法呆集生发泡（GV）期小鼠卵母细胞,将卵透明带糖蛋白3（ZP3）启动子驱动的ФC31整合酶表达载体pZP3－INT和检测qbC31整合酶位点特异性重组功能的重组质粒载体pBCPB^＋,通过显微注射导入到小鼠卵母细胞中。培养48h后,RT-PCR检测ФC31整合酶mRNA表达以及PCR检测pBCPB^＋载体发生重组的情况。结果表明：载体pZP3-INT在卵母细胞中表达ФC31整合酶mRNA;并且pBCPB^＋载体发生了位点特异性重组,提示ФC31整合酶在卵母细胞中可以介导位点特异性重组反应。     

卵母细胞特异表达φC31整合酶载体pZP3-INT的构建及其在小鼠卵母细胞中的表达

链霉菌噬菌体φC31整合酶是一种位点特异性重组酶(Site-specific recombinase,SSR),可介导链霉菌噬菌体attP位点(Phage attachment site)和链霉菌基因组attB位点(Bacterial attachment site)间的单向重组.为探讨它能否应用于卵母细胞特定基因的重组,文章采用卵巢针刺取卵法采集生发泡(GV)期小鼠卵母细胞,将卵透明带糖蛋白3(ZP3)启动子驱动φC31整合酶表达载体pZP3-INT和检测φC31整合酶位点特异性重组功能的重组质粒载体pBCPB+,通过显微注射导入到小鼠卵母细胞中.培养48 h后,RT-PCR检测φC31整合酶mRNA表达以及PCR检测pBCPB+载体发生重组的情况.结果表明:载体pzP3-INT在卵母细胞中表达φC31整合酶mRNA;并且pBCPB+载体发生了位点特异性重组,提示φC31整合酶在卵母细胞中可以介导位点特异性重组反应.     

结核分枝杆菌临床株4种耐药基因的检测与分析

结核分枝杆菌Mycobacterium tuberculsis(M.t)4种耐药基因的研究,了解耐药基因突变情况和耐药水平的关系。108例临床痰标本临床分离株均做传统梯度药敏试验和聚合酶链反应多态-单链构象多态性（PCR-SSCP）试验。结果表明耐SM（rpsL）REP(rpoB）INH(katG）EMB（embB）基因突变率分别为78.5%,68.2%,70.5%,48.6%。其中,上海高耐药株基因突变率分别为86.5%,89.3%,84.3%,35.3%。低耐药株分别为28.5%,16.5%,7.1%。EMB在低耐药区无基因突变。M.t的4种耐药基因联合检测的分析,在国内外很少报道。部分M.t的耐药由耐药基因突变所致,M.t耐药基因突变与耐药水平密切相关,且M.t基因突变绝大多数发生在高耐药区中,也有少部分在低耐区株中发生。     

河南省部分地区人类免疫缺陷病毒1型耐药性发生和演变的队列研究

目的 了解河南省某地人类免疫缺陷病毒(HIV)耐药性毒株的进化演变规律.方法 将河南省南部某地74例接受齐多夫定(AZT)+去羟肌苷(ddI)+奈韦拉平(NVP)联合抗病毒治疗的艾滋病患者纳入研究队列,分别在抗病毒治疗后3、6、12、18个月进行随访调查,通过逐一访谈了解一般情况、服药方案、服药依从性及保障措施、抗病毒治疗前后的临床表现等,同时采集14 ml EDTA抗凝静脉血,检测CD4/CD8细胞数、病毒载量及基因型耐药性.结果 核苷类反转录酶抑制剂中,发生频率最高的耐药突变位点是:67、118、151和215.治疗3、6、12、18个月时AZT耐药发生率分别为6.76%、13.51%、14.86%和9.46%,ddI的耐药发生率分别为2.70%、6.76%、8.11%和5.45%,AZT的耐药发生率高于ddI,核苷类反转录酶抑制剂的耐药性呈现出先上升后下降的趋势.非核苷类反转录酶抑制剂的耐药发生率高于核苷类反转录酶抑制剂,发生频率最高的耐药突变位点是:103和181.治疗3、6、12、18个月时,NVP耐药发生率分别为9.46%、18.92%、22.97%和32.43%.非核苷类反转录酶抑制剂呈现出持续上升的耐药发生趋势.耐药和不耐药患者的病毒载量和CD4+T淋巴细胞计数无显著性差异.服药依从性差可能是耐药发生的主要影响因素.结论 本组患者中已出现对非核苷类反转录酶抑制剂的高度耐药,服药依从性是耐药发生的主要影响因素.应加强服药的监督管理,改善患者的服药依从性.     

T66I突变提高HIV-1整合酶可溶性研究

在研究HIV-1整合酶（IN）抗药性突变T66I时,发现这一突变同时可以提高整合酶的溶解性。原核表达了IN1–288/T66I和野生型（WT）,取菌体破碎后的上清, SDS-PAGE和his标签蛋白质染色进行分析,结果表明IN1–288/T66I可溶性约是WT的2.4倍。600 ml培养基中诱导表达IN1–288/T66I/BL21,亲和层析纯化共收获蛋白质4.72 mg。用改进的ELISA方法测定IN1–288/T66I和IN1 288/F185K /C280S链转移催化活性,结果显示两种蛋白质活性基本相当。提供了有别于F185K /C280S突变的另外一种整合酶可溶性表达的途径,IN1–288/T66I重组蛋白还可以应用到整合酶抑制剂筛选中,以获取避开T66I抗药性突变的抑制剂。     

ΦC31 integrase interacts with TTRAP and inhibits NFκB activation

Phage ΦC31 integrase-mediated gene delivery is believed to be safer than using retroviral vectors since the protein confines its insertion of the target gene to a limited number of sites in mammalian genomes. To evaluate its safety in human cells, it is important to understand the interactions between this integrase and cellular proteins. Here we show that ΦC31 integrase interacts with TTRAP as presented by yeast two-hybrid and co-immunoprecipitation assays. Reducing the expression of endogenous TTRAP can increase the efficiency of ΦC31 integrase-mediated integration. A possible effect of interaction between ΦC31 integrase and TTRAP was highlighted by the fact that ΦC31 integrase inhibited the NFκB activation mediated by IL-1 in a dose-dependent manner. Because low dose of ΦC31 integrase can mediate considerable recombination events, we suggest that low dose of ΦC31 integrase be used when this integrase is applied in human cells.     

Sp100 interacts with phage ΦC31 integrase to inhibit its recombination activity

Phage ΦC31 integrase is a potential vector for the insertion of therapeutic genes into specific sites in the human genome. To understand the mechanism involved in ΦC31 integrase-mediated recombination, it is important to understand the interaction between the integrase and cellular proteins. Using a yeast two-hybrid system with pLexA-ΦC31 integrase as bait, we screened a pB42AD human fetal brain cDNA library for potential interacting cellular proteins. From the 10? independent clones that were screened, 11 potential interacting clones were isolated, of which one encoded C-terminal fragment of Sp100. The interaction between Sp100 and ΦC31 integrase was further confirmed by yeast mating and co-immunoprecipitation assays. The hybridization between a ΦC31 integrase peptide array and an HEK293 cell extract revealed that residues 81RILN84 in the N-terminus of ΦC31 integrase are responsible for the interaction with Sp100. Knocking down endogenous Sp100 with Sp100-specific siRNA increased ΦC31 integrase-mediated recombination but did not impact reporter gene expression. Therefore, endogenous Sp100 may interact with ΦC31 integrase and inhibit the efficiency of ΦC31 integrase-mediated recombination.     

Tn916 target DNA sequences bind the C-terminal domain of integrase protein with different affinities that correlate with transposon insertion frequency.

The conjugative transposon Tn916 inserts with widely different frequencies into a variety of target sites with related nucleotide sequences. The binding of chimeric proteins, consisting of maltose-binding protein fused to Tn916 integrase, to three different target sequences for Tn916 was examined by DNase I protection experiments. The C-terminal DNA binding domain of the Tn916 integrase protein was shown to protect approximately 40 bp, spanning target sites in the orfA and cat genes of the plasmid pIP501 and in the cylA gene of the plasmid pAD1. Competition binding assays showed that the affinities of the three target sites for Tn916 integrase varied over a greater than 3- but less than 10-fold range and that the cat target site bound integrase at a lower affinity than did the other two target sites. A PCR-based assay for transposition in Escherichia coli was developed to assess the frequency with which a defective minitransposon inserted into each target site. In these experiments, integrase provided in trans from a plasmid was the sole transposon-encoded protein present. This assay detected transposition into the orfA and cylA target sites but not into the cat target site. Therefore, the frequency of transposon insertion into a particular target site correlated with the affinity of the target for the integrase protein. Sequences within the target fragments similar to known Tn916 insertion sites were not protected by integrase protein. Analysis ot he electrophoretic behavior of circularly permuted sets of DNA fragments showed that all three target sites contained structural features consistent with the presence of a static bend, suggesting that these structural features in addition to the primary nucleotide sequence are necessary for integrase binding and, thus, target site activity.     

Gene insertion and replacement in Schizosaccharomyces pombe mediated by the Streptomyces bacteriophage phiC31 site-specific recombination system

The site-specific recombination system used by the Streptomyces bacteriophage phiC31 was tested in the fission yeast Schizosaccharomyces pombe. A target strain with the phage attachment site attP inserted at the leu1 locus was co-transformed with one plasmid containing the bacterial attachment site attB linked to a ura4+ marker, and a second plasmid expressing the phiC31 integrase gene. High-efficiency transformation to the Ura+ phenotype occurred when the integrase gene was expressed. Southern analysis revealed that the attB-ura4+ plasmid integrated into the chromosomal attP site. Sequence analysis showed that the attBxattP recombination was precise. In another approach, DNA with a ura4+ marker flanked by two attB sites in direct orientation was used to transform S. pombe cells bearing an attP duplication. The phiC31 integrase catalyzed two reciprocal cross-overs, resulting in a precise gene replacement. The site-specific insertions are stable, as no excision (the reverse reaction) was observed on maintenance of the integrase gene in the integrant lines. The irreversibility of the phiC31 site-specific recombination system sets it apart from other systems currently used in eukaryotic cells, which reverse readily. Deployment of the phiC31 recombination provides new opportunities for directing transgene and chromosome rearrangements in eukaryotic systems.     

Site-Specific Recombination of Temperate Myxococcus xanthus Phage Mx8: Regulation of Integrase Activity by Reversible, Covalent Modification

Temperate Myxococcus xanthus phage Mx8 integrates into the attB locus of the M. xanthus genome. The phage attachment site, attP, is required in cis for integration and lies within the int (integrase) coding sequence. Site-specific integration of Mx8 alters the 3' end of int to generate the modified intX gene, which encodes a less active form of integrase with a different C terminus. The phage-encoded (Int) form of integrase promotes attP x attB recombination more efficiently than attR x attB, attL x attB, or attB x attB recombination. The attP and attB sites share a common core. Sequences flanking both sides of the attP core within the int gene are necessary for attP function. This information shows that the directionality of the integration reaction depends on arm sequences flanking both sides of the attP core. Expression of the uoi gene immediately upstream of int inhibits integrative (attP x attB) recombination, supporting the idea that uoi encodes the Mx8 excisionase. Integrase catalyzes a reaction that alters the primary sequence of its gene; the change in the primary amino acid sequence of Mx8 integrase resulting from the reaction that it catalyzes is a novel mechanism by which the reversible, covalent modification of an enzyme is used to regulate its specific activity. The lower specific activity of the prophage-encoded IntX integrase acts to limit excisive site-specific recombination in lysogens carrying a single Mx8 prophage, which are less immune to superinfection than lysogens carrying multiple, tandem prophages. Thus, this mechanism serves to regulate Mx8 site-specific recombination and superinfection immunity coordinately and thereby to preserve the integrity of the lysogenic state.     

PhiC31 integrase mediates integration in cultured synovial cells and enhances gene expression in rabbit joints

BACKGROUND: Gene transfer to synovium in joints has been shown to be an effective approach for treating pathologies associated with rheumatoid arthritis (RA) and related joint disorders. However, the efficiency and duration of gene delivery has been limiting for successful gene therapy for arthritis. The transient gene expression that often accompanies non-viral gene delivery can be prolonged by integration of vector DNA into the host genome. We report a novel approach for non-viral gene therapy to joints that utilizes phage phiC31 integrase to bring about unidirectional genomic integration. METHODS: Rabbit and human synovial cells were co-transfected with a plasmid expressing phiC31 integrase and a plasmid containing the transgene and an attB site. Cells were cultured with or without G418 selection and the number of neo-resistant colonies or eGFP cells determined, respectively. Plasmid rescue, PCR query, and DNA sequence analysis were performed to reveal integration sites in the rabbit and human genomes. For in vivo studies, attB-reporter gene plasmids and a plasmid expressing phiC31 integrase were intra-articularly injected into rabbit knees. Joint sections were used for histological analysis of beta-gal expression, and synovial cells were isolated to measure luciferase expression. RESULTS: We demonstrated that co-transfection of a plasmid expressing phiC31 integrase with a plasmid containing the transgene and attB increased the frequency of transgene expression in rabbit synovial fibroblasts and primary human RA synoviocytes. Plasmid rescue and DNA sequence analysis of plasmid-chromosome junctions revealed integration at endogenous pseudo attP sequences in the rabbit genome, and PCR query detected integration at previously characterized integration sites in the human genome. Significantly higher levels of transgene expression were detected in vivo in rabbit knees after intra-articular injection of attB-reporter gene plasmids and a plasmid expressing phiC31 integrase. CONCLUSION: The ability of phiC31 integrase to facilitate genomic integration in synovial cells and increase transgene expression in the rabbit synovium suggests that, in combination with more efficient DNA delivery methods, this integrase system could be beneficial for treatment of rheumatoid arthritis and other joint disorders.