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PubMed1999

Efficient homologous and illegitimate recombination in the opportunistic yeast pathogen Candida glabrata.

The opportunistic pathogen Candida glabrata causes significant disease in humans. To develop genetic tools to investigate the pathogenicity of this organism, we have constructed ura3 and his3 auxotrophic strains by deleting the relevant coding regions in a C. glabrata clinical isolate. Linearized plasmids carrying a Saccharomyces cerevisiae URA3 gene efficiently transformed the ura3 auxotroph to prototrophy. Homologous recombination events were observed when the linearized plasmid carried short terminal regions homologous with the chromosome. In contrast, in the absence of any chromosomal homology, the plasmid integrated by illegitimate recombination into random sites in the genome. Sequence analysis of the target sites revealed that for the majority of illegitimate transformants there was no microhomology with the integration site. Approximately 0.25% of the insertions resulted in amino acid auxotrophy, suggesting that insertion was random at a gross level. Sequence analysis suggested that illegitimate recombination is nonrandom at the single-gene level and that the integrating plasmid has a preference for inserting into noncoding regions of the genome. Analysis of the relative numbers of homologous and illegitimate recombination events suggests that C. glabrata possesses efficient systems for both homologous and nonhomologous recombination.

Base Sequence↗

PubMed1989

Sequences in E1A proteins of human adenovirus 5 required for cell transformation, repression of a transcriptional enhancer, and induction of proliferating cell nuclear antigen.

A range of deletion and other mutants in the coding region of the E1A gene of Ad5 has been assayed for transformation of baby rat kidney (BRK) cells in cooperation with ras, repression of the SV40 enhancer, and induction of proliferating cell nuclear antigen (PCNA). Transformation efficiency was drastically reduced by deletion of residues 4-25, 36-60, or 111-138 in exon 1 of the 289 residue (289R) and 243R E1A proteins. Deletion of other residues in exon 1 had little effect. With mutants in the region unique to the 289R protein, and in exon 2, the only effect on transformation seemed to be an increased tendency of mutant transformants, compared to wt, to migrate to form secondary foci. Repression assays, performed with E1A plasmids producing only the 243R protein, showed that deletion of residues 4-25 or 36-60 inhibited repression completely. Deletion of residues 128-138 reduced repression, but deletions elsewhere in exon 1 had little effect. Deletion of residues 188-204 in exon 2 reduced repression slightly, and deletion of all of exon 2 reduced it to about one-half. It is concluded that for transformation, there are two functional domains in E1A proteins, both in exon 1, both involved in binding different cellular proteins, and both probably concerned with different transforming functions. One of these domains, involving residues 4-25 and 36-60, also functions in repression, but the role of the second in repression is much less critical. All of the deletion mutants in exon 1 induced PCNA synthesis in BRK cells. This result, together with previously published work, suggests that the active site for PCNA induction either involves residues 61-69 or 82-85 in exon 1, which have not been deleted, or it does not depend on any single limited region of the E1A proteins.

Adenovirus Early Proteins↗

PubMed1992

The RxxRxRxxC motif conserved in all Rel/kappa B proteins is essential for the DNA-binding activity and redox regulation of the v-Rel oncoprotein.

The v- and c-Rel oncoproteins bind to oligonucleotides containing kappa B motifs, form heterodimers with other members of the Rel family, and modulate expression of genes linked to kappa B motifs. Here, we report that the RxxRxRxxC motif conserved in all Rel/kappa B family proteins is absolutely required for v-Rel protein-DNA contact and its resulting transforming activity. We also demonstrate that serine substitution of the cysteine residue conserved within this motif enables v-Rel to escape redox control, thereby promoting overall DNA binding. These mutant proteins retained the ability to competitively inhibit kappa B-mediated transcriptional activation of the human immunodeficiency virus long terminal repeat but failed to efficiently transform chicken lymphoid cells both in vitro and in vivo. Our data indicate that reduction of the conserved cysteine residue in the RxxRxRxxC motif may be required for optimal DNA-protein interactions. These results provide direct biochemical evidence that the DNA-binding activity of v-Rel is subject to redox control and that the conserved cysteine residue in the RxxRxRxxC motif is critical for this regulation. These studies suggest that the DNA-binding, transcriptional, and biological activities of Rel family proteins may also be subject to redox control in vivo.

Base Sequence↗

PubMed2000

Efficient DNA subcloning through selective restriction endonuclease digestion.

Described here is a selective restriction endonuclease digestion method that eliminates the electrophoresis step that is usually used during the subcloning of new DNA sequences into typical E. coli-based plasmids. The method increases yield while decreasing laboratory resource and time utilization. By using donor and acceptor sequences that contain unique restriction sites found only outside of the intended recombination sequences, the initial digestion products can be directly combined without electrophoresis if the ligation step is followed by a selective digestion using the unique restriction enzymes before transformation. This system is based on the several order of magnitude decrease in transformation efficiency of linearized compared to circular plasmids. As an example, this method was used to obtain recombinants between a 3.6 kb acceptor plasmid and 3.0 kb insert following one ligation reaction after the failure of nine standard reactions using similar amounts of input DNA. It is particularly applicable to situations in which low subcloning efficiencies are expected. The technique can be extended to a large percentage of planned recombinations by using nonidentical compatible cohesive or blunt-ended fragments, or site-directed mutagenesis.

Cloning, Molecular↗

PubMed1989

Construction and shuttling of novel bifunctional vectors for Streptomyces spp. and Escherichia coli.

Shuttle vectors for gene transfer between Streptomyces spp. and Escherichia coli have been constructed by fusion of an artificial multicopy E. coli replicon and DNA fragments of pIJ702. Stable transfer to Streptomyces lividans was obtained. Marked differences in transformation efficiency were observed when plasmid DNA isolated from E. coli GM119 was used instead of that from strain HB101.

Base Sequence↗

PubMed1999

Stannous chloride mediates single strand breaks in plasmid DNA through reactive oxygen species formation.

Stannous ion (Sn) has been employed in nuclear medicine and in food industry. We described that Stannous Chloride (SnCl2) inactivation effect in Escherichia coli is mediated by a Fenton-like reaction. The effect of SnCl2 was studied through: (i) the alteration of plasmid topology in neutral and acidic pH by gel electrophoresis; and (ii) the transformation efficiency of an wild type E. coli strain. Treatment of plasmid DNA pUC 9.1 with SnCl2, at pH 7.4, results in DNA single-strand breaks (SSB), in a dose-dependent manner. Addition of sodium benzoate partly inhibited the DNA damage, while EDTA completely abolishes DNA-SSB. Furthermore, the ability of the plasmid to transform E. coli was reduced. At pH 1.3, SnCl2 exerts a protective effect on plasmid against HCI depurination. Our results suggest the generation of ROS, such as *OH by a Fenton-like reaction, close to the site of the lesions due to a possible complexation of stannous ion to DNA.

DNA Damage↗

PubMed1983

Complete DNA methylation does not prevent polyoma and simian virus 40 virus early gene expression.

The effect of DNA methylation on polyoma virus and simian virus 40 gene expression was investigated. For this purpose, the cytosines of all C-G dinucleotides of the viral DNAs were methylated by the use of rat liver methylase and the completeness of methylation was verified by dinucleotide analysis and restriction endonuclease treatment. The biological activity of unmethylated and fully methylated DNAs was tested by microinjecting them into tissue culture cells. The functions analyzed included early and late viral gene expression, viral DNA replication, oncogenic transformation efficiency, and virus maturation. No difference in any of these biological functions was observed between methylated and unmethylated DNA. Early gene expression of methylated DNA is not the result of demethylation because viral DNA reextracted from the injected cells, under nonpermissive conditions, retained the methylation pattern of the input DNA. In contrast, viral DNA extracted from transformed cells or from intact virus particles was partially or completely demethylated.

Antigens, Viral, Tumor↗

PubMed1986

Translation of open reading frame E5 of bovine papillomavirus is required for its transforming activity.

A series of mutations in open reading frame (ORF) E5 of bovine papillomavirus type 1 has been constructed to determine whether this putative gene is required for in vitro oncogenic transformation by viral DNA. Frameshift mutations at either of two different positions located exclusively in ORF E5 cause a substantial reduction in the ability of the cloned viral DNA to induce the appearance of transformed foci of mouse C127 cells. A genetic mapping experiment with one of the mutants indicates that this characteristic transformation defect is actually due to the constructed mutation in ORF E5. Analysis of 10 different mutants with sequence changes at a single position in the ORF showed that there is an exact correspondence between transformation-competence and the ability of the 3' half of ORF E5 to be correctly translated. The transformation defect of an ORF E5 frameshift mutant can be suppressed by a second mutation that restores the correct reading frame to most of the ORF, but not by one that restores the reading frame near the 3' end of the ORF. These results constitute strong genetic evidence that translation of ORF E5 is required for efficient transformation of mouse C127 cells by bovine papillomavirus DNA. Wild-type ORF E5 has the potential to encode a short hydrophobic protein or polypeptide domain.

Amino Acid Sequence↗

PubMed2000

comH, a novel gene essential for natural transformation of Helicobacter pylori.

Helicobacter pylori is naturally competent for transformation, but the DNA uptake system of this bacterium is only partially characterized, and nothing is known about the regulation of competence in H. pylori. To identify other components involved in transformation or competence regulation in this species, we screened a mutant library for competence-deficient mutants. This resulted in the identification of a novel, Helicobacter-specific competence gene (comH) whose function is essential for transformation of H. pylori with chromosomal DNA fragments as well as with plasmids. Complementation of comH mutants in trans completely restored competence. Unlike other transformation genes of H. pylori, comH does not belong to a known family of orthologous genes. Moreover, no significant homologs of comH were identified in currently available databases of bacterial genome sequences. The comH gene codes for a protein with an N-terminal leader sequence and is present in both highly competent and less-efficient transforming H. pylori strains. A comH homolog was found in Helicobacter acinonychis but not in Helicobacter felis and Helicobacter mustelae.

Bacterial Proteins↗

PubMed1975

Transformation of horse skin cells by type-C sarcoma viruses.

A horse skin cell line (E. Derm, NBL-6, CCL-57) was susceptible to focus formation by the Kirsten mouse sarcoma virus, feline sarcoma virus (ST stain) and the MSV pseudotypes with woolly monkey, gibbon monkey, RD-114, AT-124, baboon placenta and murine xenotropic (BALB/c 3T3 and C57L/JD) type-C viruses. Foci were detected within 5 days after infection and the transformed cells continued to produce infectious virus and group-specific antigen of their respective type-C leukemia viruses. The transformation efficiency of various type-C sarcoma viruses in horse cells was also very high.

Animals↗

PubMed1991

An autonomously replicating plasmid transforms Aspergillus nidulans at high frequency.

From an unstable Aspergillus nidulans colony, resulting from transformation with an A. nidulans gene bank, a plasmid was reisolated which transformed A. nidulans at a frequency of 20,000 transformants per 10(6) protoplasts at near saturation levels of transforming DNA. This represents a 250-fold enhancement of transformation efficiency over that found for typical integrative vectors such as pILJ16, the plasmid used in gene bank constructions. The plasmid, designated ARp1, is 11.5 kb in size, and consists of sequences derived from the 5.4-kb gene bank vector pILJ16, which carries the A. nidulans gene argB, and a 6.1-kb insert, designated AMA1. Southern analysis of transformant DNA showed ARp1 to be maintained in free form and not integrated into the chromosome. It has a mean copy number of 10-30 per haploid genome, and is mitotically unstable, being lost from 65% of asexual progeny of transformants. It shows similar transformational properties in A. niger and A. oryzae.

Aspergillus nidulans↗

PubMed2001

Stable transformation of sunflower (Helianthus annuus L.) using a non-meristematic regeneration protocol and green fluorescent protein as a vital marker.

Stable transformation of sunflower was achieved using a non-meristematic hypocotyl explant regeneration protocol of public inbred HA300B. Uniformly transformed shoots were obtained after co-cultivation with Agrobacterium tumefaciens carrying a gfp (green fluorescent protein) gene containing an intron that blocks expression of gfp in Agrobacterium. Easily detectable, bright green fluorescence of transformed tissues was used to establish an optimal regeneration and transformation procedure. By Southern blot analysis, integration of the gfp and nptll genes was confirmed. Stable transformation efficiency was 0.1%. From 68 T1 plants analyzed, 17 showed transmission of transgene DNA and 15 of them contained the intact gfp gene. Expression of gfp was detected in 10 T1 plants carrying the intact gfp gene using a fluorimetric assay or western blot analysis. Expression of the nptll gene was confirmed in 13 T1 plants. The transformation system enables the rapid transfer of agronomically important genes.

Biomarkers↗

PubMed1993

v-jun cooperates with v-erbB to transform the thrombocytic/megakaryocytic lineage.

The transforming properties of v-jun, the viral counterpart of the transcription factor AP1, were investigated in avian hematopoietic cells. Two retroviruses, called JB and JBN, expressing both v-jun and v-erbB, were constructed using an avian erythroblastosis-based vector. We show that the cooperative action of both oncogenes allowed the virus to efficiently transform bone marrow cells. No such transformation was obtained with either oncogene alone. JB-transformed bone marrow cells expressed GATA-1, TAL-1, and histone H5, suggesting that they belong to the erythrocytic/thrombocytic lineage. (Thrombocytes are the avian homologues of mammal megakaryocytes.) Moreover, after induction with phorbol 12-myristate 13-acetate JB-transformed bone marrow cells began to differentiate and synthesized high levels of platelet glycoproteins, indicating that they were of thrombocytic origin. These results were confirmed by c-ets1 analysis since this transcription factor, specifically found in cells with megakaryocytic but not erythrocytic features, was clearly detected in these cells.

Animals↗

PubMed2004

BBE02 disruption mutants of Borrelia burgdorferi B31 have a highly transformable, infectious phenotype.

We constructed highly transformable and infectious Borrelia burgdorferi B31 by inactivating BBE02, a putative restriction-modification gene on the linear plasmid lp25. The low-passage-number B31 clones 5A4 (containing all plasmids) and 5A18 (lp28-4(-) lp56(-)) were used for this study, and BBE02 was disrupted by homologous recombination. The transformation efficiency with the shuttle vector pBSV2C03::gntDeltakan was increased from <1 to approximately 10 colonies per mug of DNA for 5A4 and 5A4 BBE02::Kan(r) and from 14 to approximately 600 colonies per mug of DNA for 5A18 and 5A18 BBE02::Kan(r). lp25, which is required for infectivity in mice, was retained in BBE02 mutants transformed with pBSV2C03::gntDeltakan, but lp25 was not detected in transformants of the parental clones 5A4 and 5A18. BBE02 disruptants and pBSV2C03::gntDeltakan transformants of these clones remained infectious in C3H/HeN mice, and the 50% infective doses of the BBE02 disruptants were <10(2) organisms per mouse. The inactivation of BBE02 thus eliminates a transformation barrier for infectious B. burgdorferi B31 and will provide a valuable tool for studying the virulence factors of Lyme disease.

Animals↗

PubMed2004

DNA fragment transplacement in Saccharomyces cerevisiae: some genetic considerations.

The ability to make specific genomic alterations is an invaluable tool to researchers who use genetics and biochemistry to study problems in biology. We have investigated some of the parameters governing DNA fragment transplacement in two commonly used strains of Saccharomyces cerevisiae, S288C and W303-1A. These strains exhibited a marked difference in their capacity to take up plasmid DNA and utilize linear DNA fragments as substrates for transplacement. The contributions of transformation efficiency, length of homology, and alternative target site configuration were assessed. This analysis indicates that several genetic parameters are important for optimizing the efficiency of gene transplacement.

Base Sequence↗

PubMed1997

Synergy between the Mos/mitogen-activated protein kinase pathway and loss of p53 function in transformation and chromosome instability.

Constitutive activation of mitogen-activated protein kinase (MAPK) is a property common to many oncoproteins, including Mos, Ras, and Raf, and is essential for their transforming activities. We have shown that high levels of expression of the Mos/MAPK pathway in Swiss 3T3 fibroblast cause cells in S phase to undergo apoptosis, while cells in G1 irreversibly growth arrest. Interestingly, cells in G2 and M phases also arrest at a G1-like checkpoint after proceeding through mitosis. These cells fail to undergo cytokinesis and are binucleated. Thus, constitutive overexpression of Mos and MAPK cannot be tolerated, and fibroblasts transformed by Mos express only low levels of the mos oncogene product. Here, we show that p53 plays a key role in preventing oncogene-mediated activation of MAPK. In the absence of p53 (p53-/-), the growth arrest normally observed in wild-type p53 (p53+/+) mouse embryo fibroblasts (MEFs) is markedly reduced. The mos transformation efficiency in p53-/- MEFs is two to three orders of magnitude higher than that in p53+/+ cells, and p53-/- cells tolerate > 10-fold higher levels of both Mos and activated MAPK. Moreover, we show that, like Mos, both v-ras and v-raf oncogene products induce apoptosis in p53+/+ MEFs. These oncogenes also display a high transforming activity in p53-/- MEFs, as does a gain-of-function MAPK kinase mutant (MEK*). Thus, the p53-dependent checkpoint pathway is responsive to oncogene-mediated MAPK activation in inducing irreversible G1 growth arrest and apoptosis. Moreover, we show that the chromosome instability induced by the loss of p53 is greatly enhanced by the constitutive activation of the Mos/MAPK pathway.

3T3 Cells↗

PubMed2001

Age-dependent transformation frequency in elite wheat varieties.

Wheat is a major world crop and as such is a primary target for improvement of agronomic characteristics via genetic engineering. Optimization of transformation is essential in order to overcome the relatively low transformation frequencies encountered with wheat. Transformation of elite wheat varieties is not always successful due to variability in regeneration and transformation frequencies between varieties. In this work, two elite wheat varieties with a relatively high embryogenic capacity were transformed by particle bombardment. A strong correlation between transformation frequency and the age of wheat donor plants was observed in both varieties. The mean transformation frequency rose from 0.7% to 5% when using immature embryos from old and young donor plants, respectively. This was observed in both varieties, the best bombardments achieving up to 7.3% frequency. Using explants at an optimal developmental stage from donor plants grown under environmentally-controlled conditions has improved the reproducibility of transformation efficiency of elite wheat varieties and leads to the production of apparently phenotypically normal, fertile, transgenic plants.

Base Sequence↗

PubMed2004

[Construction of the plant expression vector with hepatitis a capsid protein fusion gene and genetic transformation of Citrus. Sinensis Osbeck].

The use of edible plants for the production and delivery of vaccine proteins could provide an economical alternative to fermentation systems. The construction of the plant expression vector pBI121-A was reported, which contained a fusion gene encoding hepatitis A capsid proteins. The gene was located between the left and right Ti border sequences under the control of CaMV35S promoter. The vector was identified via PCR and restriction enzyme analysis and was introduced into Agrobacterium tumerifacience LBA4404. The transgenic Citrus plants were produced by Agrobacterium-mediated transformation of epicotyl segments.13 putatively transformed plants through the kanamycin selection were micrografted onto the seedlings. The presence and integration of the transgene had been verified by PCR analysis. The result showed that five transformants were integrated and the transformation efficiency was 4.1%.

Citrus sinensis↗