Direct cloning of full-length mouse mitochondrial DNA using a Bacillus subtilis genome vector

The complete mouse mitochondrial genome (16.3 kb) was directly cloned into a Bacillus subtilis genome (BGM) vector. Two DNA segments of 2.06 and 2.14 kb that flank the internal 12 kb of the mitochondrial DNA (mtDNA) were subcloned into an Escherichia coli plasmid. Subsequent integration of the plasmid at the cloning locus of the BGM vector yielded a derivative specific for the targeted cloning of the internal 12-kb mtDNA region. The BGM vector took up mtDNA purified from mouse liver and integrated it by homologous recombination at the two preinstalled mtDNA-flanking sequences. The complete cloned mtDNA in the BGM vector was converted to a covalently closed circular (ccc) plasmid form via gene conversion in B. subtilis. The mtDNA carried on this plasmid was then isolated and transferred to E. coli. DNA sequence fidelity and stability through the BGM vector-mediated cloning process were confirmed.     

Efficient cloning and engineering of entire mitochondrial genomes in Escherichia coli and transfer into transcriptionally active mitochondria

We have devised an efficient method for replicating and stably maintaining entire mitochondrial genomes in Escherichia coli and have shown that we can engineer these mitochondrial DNA (mtDNA) genome clones using standard molecular biological techniques. In general, we accomplish this by inserting an E.coli replication origin and selectable marker into isolated, circular mtDNA at random locations using an in vitro transposition reaction and then transforming the modified genomes into E.coli. We tested this approach by cloning the 16.3 kb mouse mitochondrial genome and found that the resulting clones could be engineered and faithfully maintained when we used E.coli hosts that replicated them at moderately low copy numbers. When these recombinant mtDNAs were replicated at high copy numbers, however, mtDNA sequences were partially or fully deleted from the original clone. We successfully electroporated recombinant mouse mitochondrial genomes into isolated mouse mitochondria devoid of their own DNA and detected robust in organello RNA synthesis by RT-PCR. This approach for modifying mtDNA and subsequent in organello analysis of the recombinant genomes offers an attractive experimental system for studying many aspects of vertebrate mitochondrial gene expression and is a first step towards true in vivo engineering of mammalian mitochondrial genomes.     

Two autonomously replicating sequences near oli-1 gene of yeast mitochondrial DNA

We cloned two autonomously replicating sequences from a short segment of mtDNA of an oligomycin-resistant petite yeast, O-111, into a vector pYleu 12 constructed from yeast LEU 2 gene and pBR 322. These plasmids, pYmit 4 and pYmit 1, had frequencies of transformation of yeast as high as that of YEp 13, having a replicator of 2 mu DNA. They were maintained as plasmids in yeast under selective conditions and shuttled from yeast to E. coli. No evidence was obtained that these plasmids were incompatible with the wild-type mitochondrial genome. These sequences were located in intergenic regions.     

Highly efficient yeast-based in vivo DNA cloning of multiple DNA fragments and the simultaneous construction of yeast/ Escherichia coli shuttle vectors

In vivo recombinational cloning in yeast is a very efficient method. Until now, this method has been limited to experiments with yeast vectors because most animal, insect, and bacterial vectors lack yeast replication origins. We developed a new system to apply yeast-based in vivo cloning to vectors lacking yeast replication origins. Many cloning vectors are derived from the plasmid pBR322 and have a similar backbone that contains the ampicillin resistance gene and pBR322-derived replication origin for Escherichia coli. We constructed a helper plasmid pSUO that allows the in vivo conversion of a pBR322-derived vector to a yeast/E. coli shuttle vector through the use of this backbone sequence. The DNA fragment to be cloned is PCR-amplified with the addition of 40 bp of homology to a pBR322-derived vector. Cotransformation of linearized pSU0, the pBR322-derived vector, and a PCR-amplified DNA fragment, results in the conversion of the pBR322-derived vector into a yeast/E. coli shuttle vector carrying the DNA fragment of interest. Furthermore, this method is applicable to multifragment cloning, which is useful for the creation of fusion genes. Our method provides an alternative to traditional cloning methods.     

Fructose bisphosphatase of Saccharomyces cerevisiae. Cloning, disruption and regulation of the FBP1 structural gene

Fructose bisphosphatase catalyzes a key reaction of gluconeogenesis. We have cloned the fructose bisphosphatase (FBP1) structural gene from Saccharomyces cerevisiae by screening a genomic library for complementation of an Escherichia coli fbp deletion mutation. The cloned DNA expresses in E. coli a fructose bisphosphatase activity which is precipitable with antibodies specific for the yeast enzyme and is sensitive to inhibition by fructose 2,6-bisphosphate. Evidence is presented demonstrating that the entire gene, including all cis-acting regulatory sequences, has been cloned. A substitution mutation that disrupts FBP1 was incorporated into the yeast genome by transplacement to construct a fructose bisphosphatase null mutation. The fbp1 mutant strain is a hexose auxotroph, otherwise growing normally. Southern blot hybridization analysis confirmed the structure of the transplacement and demonstrated that FBP1 is present in single copy in the haploid genome. Northern blot hybridization analysis revealed an mRNA of about 1350 nucleotides, whose presence was repressible by glucose in the medium. Fructose bisphosphatase activity was not greatly overproduced when the FBP1 gene was present on a multicopy vector in yeast.     

PCR-based cloning of the complete mouse mitochondrial genome and stable engineering in <Emphasis Type="Italic">Escherichia</Emphasis> <Emphasis Type="Italic">coli</Emphasis>

We have devised a method for cloning an entire mammalian mitochondrial genome (mtDNA) in Escherichia coli using PCR-based amplification and sequential ligation. Here we test this approach by cloning the complete mouse mtDNA. The mtDNA was divided into four to five fragments based on unique restriction enzyme sites and amplified by high-fidelity long-range DNA polymerase. The synthesized fragments were cloned individually to test their toxicity in the E. coli host and then combined sequentially into a vector containing the E. coli R6K origin of DNA replication. The synthetic complete mouse mtDNA clones were replicated stably and faithfully in E. coli when maintained at moderately low copy numbers per cell. The sequence integrity of the synthetic mouse mtDNA clones was confirmed by nucleotide sequencing; no mutations or rearrangements in the genome were found. This approach can facilitate the cloning of entire mammalian mitochondrial genomes in E. coli and assist in the introduction of desired modifications into the mitochondrial genome.     

Direct Cloning of Yeast Genes from an Ordered Set of Lambda Clones in Saccharomyces Cerevisiae by Recombination in Vivo

We describe a technique that facilitates the isolation of yeast genes that are difficult to clone. This technique utilizes a plasmid vector that rescues lambda clones as yeast centromere plasmids. The source of these lambda clones is a set of clones whose location in the yeast genome has been determined by L. Riles et al. in 1993. The Esherichia coli-yeast shuttle plasmid carries URA3, ARS4 and CEN6, and contains DNA fragments from the lambda vector that flank the cloned yeast insert. When yeast is cotransformed with linearized plasmid and lambda clone DNA, Ura(+) transformants are obtained by a recombination event between the lambda clone and the plasmid vector that generates an autonomously replicating plasmid containing the cloned yeast DNA sequences. Genes whose genetic map positions are known can easily be identified and recovered in this plasmid by testing only those lambda clones that map to the relevant region of the yeast genome for their ability to complement the mutant phenotype. This technique facilitates the isolation of yeast genes that resist cloning either because (1) they are underrepresented in yeast genomic libraries amplified in E. coli, (2) they provide phenotypes that are too marginal to allow selection of the gene by genetic complementation or (3) they provide phenotypes that are laborious to score. We demonstrate the utility of this technique by isolating three genes, GAL83, SSN2 and MAK7, each of which presents one of these problems for cloning.     

Yeast shuttle and integrative vectors with multiple cloning sites suitable for construction of lacZ fusions

We report yeast/Escherichia coli shuttle vectors suitable for fusing yeast promoter and coding sequences to the lacZ gene of E. coli. The vectors contain a region of multiple unique restriction sites including EcoRI, KpnI, SmaI, BamHI, XbaI, SalI, PstI, SphI and HindIII. The region with the unique cloning sites has been introduced in both orientations with respect to lacZ and occurs proximal to the eighth codon of the gene. All the restriction sites have been phased to three different reading frames. Two series of vectors have been constructed. The first series (YEp) has two origins of replication (ori), i.e., of the yeast 2 mu circle and of the ColE1 plasmid of E. coli, and can therefore replicate autonomously in both organisms. These shuttle vectors also have the ApR gene of E. coli and either the yeast LEU2 or URA3 genes to allow for selection of both E. coli and yeast transformants. The second series of vectors (YIp) are identical in all respects to the YEp vectors except that they lack the 2 mu ori. The YIp vectors can be used to integrate lacZ fusions into yeast chromosomal DNA. None of the vectors express beta-galactosidase (beta Gal) in yeast or E. coli in the absence of inserted yeast promoter sequences. The 5'-nontranslated sequences and parts of the coding sequences of various yeast genes have been cloned into representative lacZ fusion vectors. In-frame gene fusions can be detected by beta Gal activity when either yeast or E. coli clones are plated on media containing XGal indicator. Quantitative determinations of promoter activity were made by colorimetric assay of beta Gal activity in whole cells. Fusion of the yeast CYC1 gene to lacZ in one of the vectors allowed detection of regulated expression of this gene when cells were grown under conditions of catabolite repression or derepression.     

Mitochondrial L-rRNA from Aspergillus nidulans: potential secondary structure and evolution.

The alignment of gene sequences coding for A. nidulans mitochondrial L-rRNA and E. coli 23S rRNA indicates a strong conservation of primary and potential secondary structure of both rRNA molecules, except that homologies to the 5'-terminal 5.8S-like region and the 3'-terminal 4.5S-like region of bacterial rRNA are not detectable on mtDNA. The structural organization of the A. nidulans mt L-rRNA gene corresponds to that of yeast omega + strains: both genes are interrupted by a large intron sequence (1678 and 1143 bp, respectively) and by another smaller insert (91 and 66 bp) at homologous positions within domain V. An evolutionary tree derived from conserved L-rRNA gene sequences of yeast nuclei, E. coli, maize chloroplasts and six mitochondrial species exhibits a common root of organelle and bacterial sequences separating early from the nuclear branch.     

Screening recombinant clones containing sequences homologous to Escherichia coli genes using single-stranded bacteriophage vector

Detection and isolation of Escherichia coli clones carrying vectors with foreign DNA sequences partially homologous to specific E. coli genes is difficult because denatured DNA in the host genome can hybridize with the probe. In this paper we present a procedure which simplifies this task by using bacteriophage M13 as the cloning vector. The procedure takes advantage of the secretory properties of the phage, as well as the property of nitrocellulose membrane to bind protein and single-stranded DNA but not double-stranded DNA. This procedure is shown to be effective in identifying E. coli clones containing sequences of Chlamydomonas reinhardtii chloroplast DNA that are homologous to the rpoC gene of E. coli. We suggest that this procedure can be used generally for rapid isolation of DNA sequences that are homologous to E. coli genes.     

Transgenic mice generated by pronuclear injection of a yeast artificial chromosome.

Transgenic mice have become invaluable for analysing gene function and regulation in vivo. However, the size of constructs injected has been limited by the cloning capacity of conventional vectors, a constraint that could be overcome with yeast artificial chromosomes (YACs). We investigated the feasibility of making transgenic mice with YACs by pronuclear injection of a small YAC carrying a gene encoding tyrosinase. Use of a vector with a conditional centromere allowed fifteenfold amplification of the YAC in yeast and its recovery in high yield. The albino phenotype of the recipient mice was rescued demonstrating the correct expression of the tyrosine gene from the construct. Furthermore, the telomeric sequences added by the yeast integrated into the mouse genome and did not reduce efficiency of integration. Using this technique future experiments with longer YACs will allow the expression of gene complexes such as Hox and the globin gene clusters to be analysed in transgenic animals.     

Nucleotide sequence of a wheat mitochondrial lysine tRNA gene

We present the sequence of a wheat mitochondrial (mt) lysine tRNA gene (trnK-UUU). This gene more closely resembles its E. coli counterpart than it does the corresponding gene in fungal or mammalian mtDNA. Hybridization experiments with a trnK-specific probe suggest that at least two copies of this tRNALys gene are present in the wheat mitochondrial genome.     

RNA-driven genetic changes in bacteria and in human cells

As recently demonstrated in the yeast Saccharomyces cerevisiae model organism using synthetic RNA-containing oligonucleotides (oligos), RNA can serve as a template for DNA synthesis at the chromosomal level during the process of double-strand break (DSB) repair. Herein we show that the phenomenon of RNA-mediated DNA modification and repair is not limited to yeast cells. A tract of six ribonucleotides embedded in single-strand DNA oligos corresponding to either lagging or leading strand sequences could serve as a template to correct a defective lacZ marker gene in the chromosome of the bacterium Escherichia coli. In order to test the capacity of RNA to modify DNA in mammalian cells, we utilized DNA oligos containing an embedded tract of six ribonucleotides, as well as oligos mostly made of RNA. These oligos were designed to repair a chromosomal break generated within a copy of the green fluorescent protein (GFP) gene randomly integrated into the genome of human HEK-293 cells. We show that these RNA-containing oligos can serve as templates to repair a DSB in human cells and can introduce base changes into genomic or plasmid DNA. In both E. coli and human cells, the strand bias of chromosomal gene correction by the single-strand RNA-containing oligos was the same as that obtained for the corresponding DNA molecules. Therefore, the RNA-containing oligos are not converted into a cDNA before annealing with complementary DNA. Overall, we demonstrate that in both bacterial and human cells, as in yeast, RNA sequences can have a direct role in DNA genetic modification and remodeling.     

Rapid method for altering bacterial ribosome-binding sequences for overexpression of proteins in Escherichia coli.

In an Escherichia coli expression system, two genes, one from an anaerobic intestinal bacterium and one from E. coli, were overexpressed following the alteration of ribosome-binding (Shine-Dalgarno) sequences. For both genes, the polymerase chain reaction (PCR) was used to modify the ribosome-binding sequence and, at the same time, provide restriction endonuclease sequences at each end of the gene. These restriction endonuclease sequences were used for inserting the DNA into the E. coli plasmid vector pGEM2, which has the T7 promoter upstream from its multiple cloning sites. Each chimeric plasmid, made by ligating the PCR product into pGEM2, was transformed into E. coli strain HMS174(DE3) which, when induced, produces T7 RNA polymerase for regulated overexpression. The gene isolated from the anaerobic intestinal bacterium, a 27-kDa polypeptide gene from Eubacterium sp. strain 12708, when expressed using this system, produced about one-third of the total cell protein as measured in Coomassie-stained protein gels and confirmed by Western blots with rabbit antibody. The E. coli enzyme, a 28.4-kDa tRNA methylation enzyme, was increased fivefold in activity of cell extracts over that of the best previous strain.     

单纯疱疹病毒2型糖蛋白D成熟肽基因毕赤酵母表达载体的构建及序列分析

构建单纯疱疹病毒2型包膜糖蛋白D成熟肽基因毕赤酵母表达载体,并对序列进行分析,为进行高抗原性的真核表达重组gD蛋白奠定基础。采用PCR扩增HSV2-gD成熟肽基因,将该段基因克隆于pGEM-T克隆载体,转化鉴定后,与巴斯德毕赤酵母表达载体(pPIC9K)酶切连接,转化大肠杆菌DH5α,筛选测序确定构建了pPIC9K?gD的真核表达载体,对克隆的序列进行分析,预测表达产物的理化特性及抗原性。结果显示,获得的重组的酵母表达载体pPIC9K-gD,测序结果证实为HSV2-gD成熟肽基因,序列分析其高度保守,预测蛋白分子量40.63kD,等电点pI为7.15,包含完整成熟肽分值达1.7的多个抗原决定簇。成功构建了HSV2-gD成熟肽基因的毕赤酵母表达载体。     

基因组细菌人工染色体文库(BAC)的构建及应用

细菌人工染色体 (BAC)是一种承载DNA大片段的克隆载体系统 ,用于人、动物和植物基因组文库构建。BAC具有插入片断大、嵌合率低、遗传稳定性好、易于操作等优点。BAC文库的构建是基因组较大的真核生物基因组学研究的重要基础 ,可用于真核生物重要基因及全基因组物理作图、重要性状基因的图位克隆、基因结构及功能分析。本文主要综述了细菌人工染色体的构建与其鉴定 ,及其在物理图谱构建、图位克隆、转基因技术等研究上的应用。