| 1. |
- Szymanski, J. J., et al.
(författare)
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MEGA : A search for the decay mu –> e gamma
- 1994
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Ingår i: Intersections between particle and nuclear physics. Proceedings, 5th Conference, St. Petersburg, USA, May 31-June 6, 1994. ; , s. 789-792
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Konferensbidrag (refereegranskat)
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| 2. |
- Amann, F., et al.
(författare)
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A search for murarregamma at the level of 10-13
- 1991
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Ingår i: Proceedings of the 25th International Conference on High Energy Physics. - 9810024347 ; , s. 1070-1071
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Konferensbidrag (refereegranskat)abstract
- The MEGA experiment, which is a search for the decay murarregamma with a branching ratio sensitivity of about 10-13, employs highly modular, fast detectors, state-of-the-art electronics, and a staged trigger with on-line filters. The detectors are contained in a 1.5-T solenoidal field produced by a superconducting magnet. Positrons are confined to the central region and are measured by a set of thin MWPCs. Photons are measured by one of four layers of pair spectrometers in the outer region. Most aspects of the design have been validated in engineering runs; data taking will begin in 1990 with much of the electron arm and one pair spectrometer layer installed.
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| 3. |
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| 4. |
- Kim, A.S., et al.
(författare)
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Fracture strength testing of δ-alumina fibres with variable diameters and lengths
- 1993
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Ingår i: Composites Science And Technology. - 0266-3538 .- 1879-1050. ; 47:4, s. 331-333
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Tidskriftsartikel (refereegranskat)abstract
- Tensile tests were performed on individual δ-alumina fibres (Saffil, RF grade). The results revealed a large scatter in strengths and a clear dependence of the fracture strength on the specimen volume. The tests were evaluated on the basis of the Weibull probability function, a special modification of the Weibull analysis being developed that successfully copes with the problem of testing fibres with various diameters and test lengths. For the sample studied the Weibull modulus, m, was found to be 2·2, with a scaling constant δ0 = 6·0 MPa (units of volume mm3; i.e. V0 = 1 mm3).
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| 5. |
- Egholm, M., et al.
(författare)
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PNA HYBRIDIZES TO COMPLEMENTARY OLIGONUCLEOTIDES OBEYING THE WATSON-CRICK HYDROGEN-BONDING RULES
- 1993
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 365:6446, s. 566-568
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Tidskriftsartikel (refereegranskat)abstract
- DNA ANALOGUES are currently being intensely investigated owing to their potential as gene-targeted drugs1-3. Furthermore, their properties and interaction with DNA and RNA could provide a better understanding of the structural features of natural DNA that determine its unique chemical, biological and genetic properties3,4. We recently designed a DNA analogue, PNA, in which the backbone is structurally homomorphous with the deoxyribose backbone and consists of N-(2-aminoethyl)glycine units to which the nucleobases are attached5-9. We showed that PNA oligomers containing solely thymine and cytosine can hybridize to complementary oligonucleotides, presumably by forming Watson-Crick-Hoogsteen (PNA)2-DNA triplexes, which are much more stable than the corresponding DNA-DNA duplexes5-7, and bind to double-stranded DNA by strand displacement5,8. We report here that PNA containing all four natural nucleobases hybridizes to complementary oligonucleotides obeying the Watson-Crick base-pairing rules, and thus is a true DNA mimic in terms of base-pair recognition.
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| 6. |
- Eriksson, M., et al.
(författare)
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LOCATION OF EXCIMER-FORMING ADDUCTS OF (+)-ANTI-BENZO A PYRENE DIOL EPOXIDE IN DNA
- 1993
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 115:5, s. 1639-1644
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Tidskriftsartikel (refereegranskat)abstract
- Covalent adducts of the carcinogenic polycyclic aromatic hydrocarbon (+)-anti-benzo[a]pyrene 7,8-dihydrodiol 9,10-epoxide ((+)-anti-BPDE) in polynucleotides have been studied by fluorescence spectroscopy. The pyrenyl chromophores of the BPDE adducts, linked by the C10 atom to the exocyclic nitrogen of guanine, interact in the photoexcited state, as evidenced by excimer fluorescence. Strong BPDE excimer fluorescence is observed in the alternating poly(dGdC).poly(dGdC) sequence, whereas it is weak in the homopolymeric poly(dG).poly(dC) and in calf thymus DNA. No excimer fluorescence is observed for the BPDE adducts in poly(dAdC).poly(dGdT) or poly(dAdG).poly(dCdT). It is concluded that the formation of BPDE excimers in polynucleotides requires binding to guanines on different strands on consecutive basepairs. The experimental results are supported by graphics modeling and energy minimization of BPDE adducts in various oligonucleotide sequences. The results show that the most favorable arrangement for excimer formation of the BPDE-dG adducts is in a 5'(dCdG-BPDE).5'(dCdG-BPDE) sequence, where the pyrenyl chromophores interact in the minor groove.
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| 7. |
- Wittung, Pernilla, 1968, et al.
(författare)
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INTERACTIONS BETWEEN DNA-MOLECULES BOUND TO RECA FILAMENT - EFFECTS OF BASE COMPLEMENTARITY
- 1994
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 269:8, s. 5799-5803
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Tidskriftsartikel (refereegranskat)abstract
- To gain information about the mechanism of RecA-promoted strand exchange reactions in genetic recombination, we have investigated the environment of and interactions between DNA strands accommodated in complexes with Beck protein. DNA bound in different sites in the Reck filament was tested by adding stoichiometric amounts of DNAs of variable base compositions. For this purpose, poly(dA) labeled by fluorescent benzo(a)pyrenediol epoxide (BPDE), which binds covalently to N-6 of adenine, was used. The fluorescence intensity, anisotropy, and quenching by acrylamide provide information about the DNA environment in the complexes with Reck In the absence of extra DNA, binding of Reck to BPDE-poly(dA) only slightly affects both the intensity of the BPDE fluorescence and the accessibility of BPDE to acrylamide. However, a strongly increased fluorescence anisotropy shows that the mobility of the BPDE fluorophore is restricted in the Reck complex. Binding of a second and third single-stranded DNA to the RecA.BPDE-poly(dA) complex reduces the fluorescence intensity in a manner that depends on base complementarity. The change is large when the second and third DNAs are poly(dT), i.e. complementary to the already bound poly(dA) strand. In such a complex, the accessibility of BPDE to quencher is also reduced. When BPDE-poly(dA) was added as the second or third DNA in the Reck filament, the fluorescence intensity became smaller when the earlier bound DNA was complementary to the added DNA. These results indicate that all three DNA strands are interacting with each other in the Beck filament. BPDE-modified poly(dA) forms a duplex with poly(dT), whereupon the fluorescence of BPDE is strongly decreased. Binding of Reck to this duplex DNA increases the BPDE fluorescence, suggesting a destabilization of the duplex. Finally, we also find indications of base complementary interactions between single-stranded and double-stranded DNAs bound to the Beck filament.
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| 8. |
- Wittung, Pernilla, 1968, et al.
(författare)
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INTERACTIONS OF DNA-BINDING LIGANDS WITH PNA DNA HYBRIDS
- 1994
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Ingår i: Nucleic Acids Research. - : Oxford University Press (OUP). - 0305-1048 .- 1362-4962. ; 22:24, s. 5371-5377
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Tidskriftsartikel (refereegranskat)abstract
- The interactions of two representative mixed-sequence (one with an AT-stretch) PNA - DNA duplexes (10 or 15 base-pairs) and a PNA(2)/DNA tripler with the DNA binding reagents distamycin A, 4',6-diamidino-2-phenylindole (DAPI), ethidium bromide, 8-methoxy-psoralen and the Delta and Lambda enantiomers of Ru(phen)(2)-dppz(2+) have been investigated using optical spectroscopic methods. The behaviour of these reagents versus two RNA-PNA duplexes has also been investigated. With triple helical poly(dA)/(H-T-10-Lys-NH2)(2) no significant intercalative binding was detected for any of the DNA intercalators, whereas DAPI, a DNA minor groove binder, was found to exhibit a circular dichroism with a positive sign and amplitude consistent with minor groove binding. Similarly, a PNA-DNA duplex containing a central AATA motif, a typical minor groove binding site for the DNA minor groove binders distamycin A and DAPI, showed binding for both of these drugs, though with strongly reduced affinity. No important interactions were found for any of the ligands with a RNA-DNA duplex consisting of a ten base-pair mixed purine-pyrimidine sequence with only two AT base-pairs in the centre. Nor did any of the ligands show any detectable binding to the PNA-PNA duplexes (one containing an AATT motif). Various PNA derivatives with extentions of the backbone, believed to increase the flexibility of the duplex to opening of an intercalation slot, were tested for intercalation of ethidium bromide or 8-methoxypsoralen into the mixed sequence PNA-DNA duplex, however, without any observation of improved binding. The importance of the ionic contribution of the deoxyribose phosphate backbone, versus interactions with the nucleobases, for drug binding to DNA is discussed in the light of these findings.
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