排序方式: 共有48条查询结果,搜索用时 15 毫秒
1.
2.
Yosef I Bloushtain N Shapira M Qimron U 《Applied and environmental microbiology》2004,70(12):7156-7160
We have developed a simple method for single-step cloning of any PCR product into a plasmid. A novel selection principle has been applied, in which activation of a drug selection marker is achieved following homologous recombination. In this method a DNA fragment is amplified by PCR with standard oligonucleotides that contain flanking tails derived from the host plasmid and the complete lambdaPR or rrnA1 promoter regions. The resulting PCR product is then electroporated into an Escherichia coli strain harboring both the phage lambda Red functions and the host plasmid. Upon homologous recombination of the PCR fragment into the plasmid, expression of a drug selection marker is fully induced due to restoration of its truncated promoter, thus allowing appropriate selection. Recombinant plasmid vectors encoding beta-galactosidase and neomycin phosphotransferase were constructed by using this method in two well-known Red systems. This cloning strategy significantly reduces both the time and costs associated with cloning procedures. 相似文献
3.
Eight wooden objects were found at Ohalo II, a submerged and well-preserved site in the Sea of Galilee, Israel. The fisher-hunter-gatherers' site has been radiometrically dated to 22,500-23,500 (cal BP) with 45 assays read by four laboratories. The wooden objects were found on brush-hut floors. They include a bark plank with polish and use signs, pencil-shaped specimens with longitudinal shavings, and other types that may have been decorative or symbolic. One incised wooden object is identical in size and incision pattern to a gazelle bone implement found in a grave, behind a human skull. The recovered wooden objects are not directly related to hunting, gathering, or fishing, and frustratingly, there are no remains of bows, arrows, spears, handles, or other such items. Nonetheless, the objects present a wide repertoire in terms of size, shape, and possible function. The new finds add to the growing body of evidence concerning the use of perishable materials during the Upper Paleolithic. 相似文献
4.
The clustered regularly interspaced short palindromic repeats and their associated proteins (CRISPR/Cas) constitute a recently identified prokaryotic defense mechanism against invading nucleic acids. Activity of the CRISPR/Cas system comprises of three steps: (i) insertion of alien DNA sequences into the CRISPR array to prevent future attacks, in a process called 'adaptation', (ii) expression of the relevant proteins, as well as expression and processing of the array, followed by (iii) RNA-mediated interference with the alien nucleic acid. Here we describe a robust assay in Escherichia coli to explore the hitherto least-studied process, adaptation. We identify essential genes and DNA elements in the leader sequence and in the array which are essential for the adaptation step. We also provide mechanistic insights on the insertion of the repeat-spacer unit by showing that the first repeat serves as the template for the newly inserted repeat. Taken together, our results elucidate fundamental steps in the adaptation process of the CRISPR/Cas system. 相似文献
5.
6.
7.
Intra-specific competition with a primary focus on root competition between plants living in an area with low resource levels, was studied using the natural monotypic population of a desert annual plantEremobium aegyptiacum (Cruciferae). We tested the effect of neighboring distance on shoot and root biomass, and such root parameters as root length, diameter of root neck, number of first order lateral roots and number of lateral roots per unit of main root length. Our results indicate a strong negative relationship between neighboring plant density and such plant parameters as shoot and root biomass, and root neck diameter. The number of first order lateral roots and the number of lateral roots per unit of main root length were negatively related to the distance between neighboring plants. Contrary to predictions, there was no influence of competition on node distribution: neither root overlap nor root avoidance was observed in pairs of adjacent plants. 相似文献
8.
We show that phage lysogenization, lysogens, and prophage induction are all targeted by CRISPR. The results demonstrate that genomic DNA is not immune to the CRISPR system, that the CRISPR system does not require noncytoplasmic elements, and that the system protects from phages entering and exiting the lysogenic cycle. 相似文献
9.
Automatic scanning of interphase FISH for prenatal diagnosis in uncultured amniocytes 总被引:4,自引:0,他引:4
Lev D Daniely M Zudik A Preisler E Hoffmann N Kaplan T Raz U Yanoov-Sharav M Vinkler H Malinger G 《Genetic testing》2005,9(1):41-47
Fluorescence in situ hybridization (FISH) of uncultured amniocytes using chromosome-specific DNA probes offers the opportunity for rapid aneuploidy screening. Between 80 and 95% of all chromosomal disorders expected in the second trimester of pregnancy can be discovered within 24 hr if DNA probes specific for chromosomes 21, 18, 13, X, and Y are used. Rapid results are crucial for clinical decision-making and are helpful in decreasing the anxiety level in most patients. One of the major factors that have been preventing the rapid FISH test from being broadly incorporated into the clinical setting is the limited staff in the cytogenetics laboratories. The present study demonstrates the use of an automated scanning system (Duet, BioView Ltd. Rehovot, Israel) for analyzing FISH in uncultured amniocytes. Fifty-six amniotic fluid samples were evaluated in parallel by karyotyping, manual FISH analysis, and automatic FISH scanning. Automatic scanning provided accurate results compared to both manual FISH scoring and karyotype analysis. The correlation between automatic and manual FISH scanning was found to be very high (r = 0.9, p < 0.0001). The availability of automation for aneuploidy screening in amniotic fluid samples will enable offering this test to a broader patient population while providing fast and reliable results. 相似文献
10.
Gilis M Grauby O Willenz P Dubois P Legras L Heresanu V Baronnet A 《Journal of structural biology》2011,(3):315-329
The massive basal skeleton of a few remnant living hypercalcified sponges rediscovered since the 1960s are valuable representatives of ancient calcium carbonate biomineralization mechanisms in basal Metazoa. A multi-scale mineralogical characterization of the easily accessible Mediterranean living hypercalcified sponge belonging to Calcarea, Petrobiona massiliana (Vacelet and Lévi, 1958), was conducted. Oriented observations in light and electron microscopy of mature and growing areas of the Mg-calcite basal skeleton were combined in order to describe all structural levels from the submicronic to the macroscopic scale. The smallest units produced are ca. 50–100 nm grains that are in a mushy amorphous state before their crystallization. Selected area electron diffraction (SAED) further demonstrated that submicronic grains are assembled into crystallographically coherent clusters or fibers, the latter are even laterally associated into single-crystal bundles. A model of crystallization propagation through amorphous submicronic granular units is proposed to explain the formation of coherent micron-scale structural units. Finally, XRD and EELS analyses highlighted, respectively, inter-individual variation of skeletal Mg contents and heterogeneous spatial distribution of Ca ions in skeletal fibers. All mineralogical features presented here cannot be explained by classical inorganic crystallization principles in super-saturated solutions, but rather underlined a highly biologically regulated formation of the basal skeleton. This study extending recent observations on corals, mollusk and echinoderms confirms that occurrence of submicronic granular units and a possible transient amorphous precursor phase in calcium carbonate skeletons is a common biomineralization strategy already selected by basal metazoans. 相似文献