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- Guo, YQ, et al.
(författare)
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The crystallographic and magnetoresistance of CaF2 doped Nd0.67Sr0.33MnO3 compounds
- 1999
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Ingår i: JOURNAL OF SOLID STATE CHEMISTRY. - : ACADEMIC PRESS INC. - 0022-4596. ; 148:2, s. 236-241
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Tidskriftsartikel (refereegranskat)abstract
- We have studied crystal structures and the giant magnetoresistance of fluoride Nd0.67Sr0.33MnO3 compounds, The experimental results show that the CaF2 dopant can stabilize the original crystal structure of Nd0.67Sr0.33MnO3 compounds. The lattice spacings
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- Liu, Li, et al.
(författare)
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Hereditary absence of complement C5 in adult mice influences Wallerian degeneration, but not retrograde responses, following injury to peripheral nerve
- 1999
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Ingår i: Journal of the peripheral nervous system. - 1085-9489 .- 1529-8027. ; 4:2, s. 123-133
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Tidskriftsartikel (refereegranskat)abstract
- We have examined the role of complement component 5 (C5) in peripheral nerve fiber degeneration and regeneration, as well as in glial and neuronal cell responses in the central nervous system (CNS). Adult congenic mice lacking C5 (C5(-)) and the corresponding normal strain (C5(+)) were used. Macrophage recruitment as well as axonal and myelin sheath elimination were delayed from 1 to 21 days postinjury in C5(-) mice compared to the C5(+) group after sciatic nerve crush. Despite this, recovery of motor function was not delayed. In the CNS, microglial cells and astrocytes responded in the same way from 3 to 21 days after sciatic nerve injury in C5(-) and C5(+) mice, and the extent of neuron death following hypoglossal nerve avulsion was the same in both groups. These findings suggest that C5 and/or its derivatives play an important role in initiating the recruitment of macrophages to the injured nerve and, probably indirectly, in early remyelination of regenerating axons, but does not influence the longterm functional restoration or axotomy-induced nerve cell death. C5-derived molecules do not appear to participate in central glial cell responses to peripheral nerve injury. These findings elucidate new aspects on the functional role of the complement system in the peripheral nervous system following peripheral nerve injury.
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| 7. |
- Tao, Liu, 1965-
(författare)
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Interactions of satellite phage P4 with its helpers : P2 and WΦ phages
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Bacteriophage P4 is a defective phage that needs a helper phage to grow lytically, since it lacks structural genes and genes encoding host cell lysis functions. P4 has the capacity to derepress the unrelated prophage P2, or its relatives after infection, thereby getting access to the late functions of the helper. The P4egene product (E protein) mediates this process via a derepression mechanism.In this work, the E protein is identified as a 10.8 kDa polypeptide, is shown to be the only P4 encoded protein required to derepress prophage P2, leading to in situ P2 DNA replication. The E has no DNA-binding activity. However it is able to interact with the P2 C repressor as shown in the yeast two-hybrid assay system. Analysis in a two-plasmid derepression system has shown that induction of the E results in a switch of P2 transcription from the lysogenic to the lytic mode. This implies that the E protein functions as an anti-repressor.The P2 C repressor acts as a dimer. The E protein is also shown to be a dimer in vivo. The E protein only marginally affects dimerisation of C, but the presence of C enhances multimeric forms of E protein. Furthermore, the binding of the C protein to its operator is inhibited by E in vitro. This indicates that the anti-repressor function of E is mediated by the formation of multimeric complexes of E and C that interferes with binding of C to its operator.The P2 sos mutation makes the P2 prophage resistant to derepression by P4. The Sos protein, which is shown not to interact with E, has an amino acid substitution of T67I and it is located within the presumed E binding epitope from 60 to 70 aa of the C-terminal part of the C protein. This supports the hypothesis that this part of the C protein is involved in interacting with the E protein.By in vitro mutagenesis,esuppressor mutations that overcome the resistance of Sos are isolated. A double mutant, E D65V+F68S, is able to interact with Sos in the yeast two-hybrid system but unable to derepress prophage P2 in the presence of Sos in the two-plasmid system. A single mutation, E D65V, has however lost the capacity to derepress the prophage P2 from the lysogenic to the lytic mode in the two-plasmid system. This indicates that amino acid 65 in E is important for its interaction with the C repressor.Moreover, P4 E can derepress the P2-related phage WFthat is heteroimmune to P2. The DNA sequences of the whole early control region of phage WFhave been determined. The transcriptional switch region of WFphage has a similar arrangement as those of P2, and P2-related phages186 and HP1. WFphage exploits similar strategy to control the lytic versus lysogenic development. The interaction between P4 and WF, however, is only one way, i.e. P4 is able to derepress WFphage but not the other way around.
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