1,720,970 research outputs found
Cre/loxP-mediated excision and amplification of large segments of Escherichia coli genome
No full textAn alternative to conventional DNA cloning: in vivo excision and amplification of large genomic segments by Cre/loxP site-specific recombination
No full textCre/loxP-mediated excision and amplification of large segments of the Escherichia coli genome
No full textThe isolation and amplification of large, predetermined segments of a genome from its host have been explored. The prototype of our approach was the excisional replication of some viruses such as the h-lysogen. Similar machinery was used to excise and amplify large genomic segments of Escherichia coli in its host. Two loxP sequences for a site-specific recombinase Cre, together with a conditional replication origin (pi-dependent gamma-ori), were inserted into the genome by homologous recombination at predetermined sites, 50-100 kb apart. Cre and pir200 which encodes the site-specific recombinase Cre and an ori-specific replication protein pi, respectively, were also introduced into the genome. The predetermined genomic segments flanked by the loxP sequences were excised and amplified upon induction of the cre and pir200 genes which were under the control of the tet promoter. This excised and amplified DNA could be easily purified as a large plasmid. This procedure can provide an alternative to conventional cloning methods by obtaining predetermined large genomic segments directly from the original organisms. In this study, using the Cre/loxP site-specific recombination and pi/gamma-ori replication system of plasmid R6K, a procedure was devised that could isolate a large segment of the E. coli genome and demonstrated the feasibility of the procedure by excising and amplifying the 50-kb trg-narZ and 100-kb trg-hipA regions of the E. coli W3110 genome. (C) 1998 Elsevier Science B.V
Antioxidants increase gene transfection efficiency of electroporation in B lymphoma cells
No full textTreatments of B lymphoma cells with dimethyl sulfoxide, nitric oxide, N-acetylcysteine, or pencillamine increased the gene transfection efficiency of electroporation (similar to 8-fold) without affecting cell viability. Decrease of electro-induced oxidative stress may explain antioxidant-increased electroporation efficiency
An Efficient Image Segmentation Technique To Identify Target Areas From Large-Sized Monochrome Images
No full textCre/loxP-mediated in vivo excision and amplification of large genomic segments of S.cerevisiae and an attempt their amplification using the Fip/FRT/2 mu ori system
No full textA HYBRID KNOWLEDGE-BASED APPROACH TO INFORMATION-RETRIEVAL
No full textFrom a couple of years ago, extensive research efforts have been devoted to the knowledge-based approach to information retrieval. These are usually based on thesauri that admit a variety of relations between control vocabularies called index terms. However, there have been few systems to offer sufficient functions enough to convey domain dependent knowledge as well as domain independent one in storing and retrieving information. This paper proposes a knowledge-based approach that facilitates not only domain independent knowledge but domain dependent one to be represented in the context of information retrieval in a simple and structured manner. It can be accomplished by separating the store of the knowledge into two boxes: domain independent knowledge Box (Ibox) and domain dependent knowledge Box (Dbox). Ibox is used as a graph-based thesaurus that permits "is-a" relation between index terms. Dbox describes domain-specific information, such as synonym relationship, some term relationships other than "is-e relation, and generation rules for complex compound phrases. Dbox is used as the front-end to Ibox that helps to convert the arbitrary terminology given by an IR user to the index terms implied in Ibox and reflects domain dependent knowledge. The query evaluation procedure QEP retrieves the documents relevant to a query given as Boolean form, interacting with Ibox and Dbox. It, first, retrieves all related documents and takes the ones of highest rank by Rada's algorithm. We show that Rada's algorithm does not raise discontinuity near zero, nor counter-intuitive result in QEP, while it does in general situation
Cre/loxP-mediated in vivo excision of large segments from yeast genome and their amplification based on the 2 mu m plasmid-derived system
No full textIn vivo excision and amplification of pre-determined, large genomic segments, directly from the genome of a natural host, provides an alternative to conventional cloning in foreign vectors. Using this approach, we have devised an in vivo procedure for excising large segments of Saccharomyces cerevisiae genome using Cre/loxP system of bacteriophage P1, followed by amplification of excised circles, as based on the yeast 2 mu m plasmid-derived ori and Flp/FRT machinery. To provide the excision and replication enzymes, trans-acting genes cre and FLP, which were under a very tight control of GAL1 and GAL10 promoters; respectively, were inserted by homologous recombination into the URA3 gene on chromosome V. Two parallel loxP sequences, which serve as the recognition sites for the Cre recombinase, were also integrated into the genome at pre-determined sites that are 50-100 kb apart. Moreover, 2 mu m ori, REP3 and two inverted FRTs, which serve as a conditional replication system, were also integrated between the loxP sites. The strain carrying all these inserted elements was perfectly stable. Only after the induction by galactose of the Cre excision function, the genomic segment flanked by two loxP sites was excised and circularized. Applying this procedure, the 50-kb LEU2-YCR011c and 100-kb LEU2-YCR035c regions of chromosome III were successfully excised from the S. cerevisiae genome, whereas the 2 mu m ori, as aided by FRT/Flp, provided the amplification function. Such excised and amplified genomic segments can be used for the sequencing and functional analysis of any yeast genes. (C) 1998 Elsevier Science B.V. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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