| 51. |
- Francis, Matthew, 1969-, et al.
(författare)
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A study of the YopD-LcrH interaction from Yersinia pseudotuberculosis reveals a role for hydrophobic residues within the amphipathic domain of YopD
- 2000
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Ingår i: Molecular Microbiology. - : Blackwell Publishing. - 0950-382X .- 1365-2958. ; 38:1, s. 85-102
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Tidskriftsartikel (refereegranskat)abstract
- The enteropathogen Yersinia pseudotuberculosis is a model system used to study the molecular mechanisms by which Gram-negative pathogens translocate effector proteins into target eukaryotic cells by a common type III secretion machine. Of the numerous proteins produced by Y. pseudotuberculosis that act in concert to establish an infection, YopD (Yersiniaouter protein D) is a crucial component essential for yop regulation and Yop effector translocation. In this study, we describe the mechanisms by which YopD functions to control these processes. With the aid of the yeast two-hybrid system, we investigated the interaction between YopD and the cognate chaperone LcrH. We confirmed that non-secreted LcrH is necessary for YopD stabilization before secretion, presumably by forming a complex with YopD in the bacterial cytoplasm. At least in yeast, this complex depends upon the N-terminal domain and a C-terminal amphipathic α-helical domain of YopD. Introduction of amino acid substitutions within the hydrophobic side of the amphipathic α-helix abolished the YopD–LcrH interaction, indicating that hydrophobic, as opposed to electrostatic, forces of attraction are important for this process. Suppressor mutations isolated within LcrH could compensate for defects in the amphipathic domain of YopD to restore binding. Isolation of LcrH mutants unable to interact with wild-type YopD revealed no single domain responsible for YopD binding. The YopD and LcrH mutants generated in this study will be relevant tools for understanding YopD function during a Yersinia infection.
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| 52. |
- Gulliksson, Mårten, et al.
(författare)
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Perturbation identities for regularized Tikhonov inverses and weighted pseudoinverses
- 2000
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Ingår i: Bit: numerical mathematics. - 0006-3835. ; 40:3, s. 513-523
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Tidskriftsartikel (refereegranskat)abstract
- e consider the perturbation analysis of two important problems for solving ill-conditioned or rank-deficient linear least squares problems. The Tikhonov regularized problem is a linear least squares problem with a regularization term balancing the size of the residual against the size of the weighted solution. The weight matrix can be a non-square matrix (usually with fewer rows than columns). The minimum-norm problem is the minimization of the size of the weighted solutions given by the set of solutions to the, possibly rank-deficient, linear least squares problem. It is well known that the solution of the Tikhonov problem tends to the minimum-norm solution as the regularization parameter of the Tikhonov problem tends to zero. Using this fact and the generalized singular value decomposition enable us to make a perturbation analysis of the minimum-norm problem with perturbation results for the Tikhonov problem. From the analysis we attain perturbation identities for Tikhonov inverses and weighted pseudoinverses.
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| 53. |
- Gulliksson, Mårten, et al.
(författare)
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Perturbation theory for generalized and constrained linear least squares
- 2000
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Ingår i: Numerical Linear Algebra with Applications. - 1070-5325. ; 7:4, s. 181-195
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Tidskriftsartikel (refereegranskat)abstract
- The perturbation analysis of weighted and constrained rank-deficient linear least squares is difficult without the use of the augmented system of equations. In this paper a general form of the augmented system is used to get simple perturbation identities and perturbation bounds for the general linear least squares problem both for the full-rank and rank-deficient problem. Perturbation identities for the rank-deficient weighted and constrained case are found as a special case. Interesting perturbation bounds and condition numbers are derived that may be useful when considering the stability of a solution of the rank-deficient general least squares problem. Copyright © 2000 John Wiley & Sons, Ltd.
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| 54. |
- Gulliksson, Mårten, et al.
(författare)
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The use and properties of Tikhonov filter matrices.
- 2000
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Ingår i: SIAM Journal on Matrix Analysis and Applications. - 0895-4798. ; 22:1, s. 276-281
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Tidskriftsartikel (refereegranskat)abstract
- We consider the concept of Tikhonov filter matrices in connection with discrete ill-posed and rank-deficient linear problems. Important properties of the Tikhonov filter matrices are given together with their filtering and regularization effects. We also present new perturbation identities for the Tikhonov regularized linear least squares problem using filter matrices generalizing well-known perturbation identities for the linear least squares problem and pseudoinverses.
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| 55. |
- Hedengren, Marika, et al.
(författare)
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Expression and evolution of the Drosophila attacin/diptericin gene family.
- 2000
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Ingår i: Biochem Biophys Res Commun. - : Elsevier BV. - 0006-291X. ; 279:2, s. 574-81
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Tidskriftsartikel (refereegranskat)abstract
- We describe the genes for three new glycine-rich antimicrobial peptides in Drosophila, two attacins (AttC and AttD) and one diptericin (DptB). Their structures support the proposal that these glycine-rich antimicrobial peptides evolved from a common ancestor and are probably also related to proline-rich peptides such as drosocin. AttC is similar to the nearby AttA and AttB genes. AttD is more divergent and located on a different chromosome. Intriguingly, AttD may encode an intracellular attacin. DptB is linked in tandem to the closely related Diptericin. However, the DptB gene product contains a furin-like cleavage site and may be processed in an attacin-like fashion. All attacin and diptericin genes are induced after bacterial challenge. This induction is reduced in imd mutants, and unexpectedly also in Tl(-) mutants. The 18w mutation particularly affects the induction of AttC, which may be a useful marker for 18w signaling.
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| 56. |
- Henfridsson, Ola, et al.
(författare)
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Barriers to learning: on organizational defenses and vicious circles in technological adaptation
- 2000
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Ingår i: Accounting, Management and Information Technologies. - 0959-8022. ; 10:1, s. 33-52
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Tidskriftsartikel (refereegranskat)abstract
- On the basis of an interpretive case study, the authors explore the learning implications of introducing First Class in a social services department. The investigated case illustrates how learning efforts easily result in ''vicious circles''; the more learning is sought after, the more solid are the barriers to learning. In this case, the existence of certain organizational virtues - the learning organization and the notion of the professional social worker - were observed to have negative learning implications. Paradoxically, at the espoused level, these two virtues can be understood as healthy signs, although their existence as only virtues makes them basically opposed to learning. The results of this study contribute to existing theory about discontinuity in technological adaptation.
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| 57. |
- Hollander, Anna, et al.
(författare)
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Röster i rätten
- 2000
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Ingår i: Kulturella perspektiv - Svensk etnologisk tidskrift. - Umeå : Föreningen Kulturella perspektiv. - 1102-7908. ; :2, s. 35-40
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Voices in CourtIn the ongoing project: Therapist and adverse party- cour! hearings about coercive intervention, weanalyze the communication process in court hearingsconcerning cases where citizens are subjectedto coercive measures (compulsory care for psychiatricpatients and drug abusers, social authorities'interventions to separate children from theirparents). The primary purpose is to analyze thedilemma ofbalancing two seemingly incompatibleroles for chief psychiatrists and social workers: tobe "on the client's side" in clinical and social worksettings, while acting as a formal adverse party tothe client in the courtroom.
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| 58. |
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| 59. |
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| 60. |
- Jansson, Roland, 1967-, et al.
(författare)
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Effects of river regulation on river-margin vegetation : A comparison of eight boreal rivers
- 2000
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Ingår i: Ecological Applications. - 1051-0761 .- 1939-5582. ; 10:1, s. 203-224
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Tidskriftsartikel (refereegranskat)abstract
- Regulation and fragmentation by dams belong to the most widespread deliberate impacts of humans on the world's rivers, especially in the Northern Hemisphere. We evaluated the effects of hydroelectric development by comparing the flora of vascular plants in 200-m-long reaches of river margin distributed along eight entire rivers in northern Sweden. Four of these rivers were free-flowing, and four were strongly regulated for hydroelectric purposes. First, we compared species diversity per site between entire free-flowing and regulated rivers. To reduce the effects of natural, between-river variation, we compared adjacent rivers. One regulated river had lower plant species richness and cover than two adjacent free-flowing ones, whereas two other parallel rivers, one regulated and another free-flowing, did not differ significantly. Second, river-margin vegetation responded differently to different types of regulated water-level regimes. Both along run-of-river impoundments, with small but daily water-level fluctuations, and along storage reservoirs, with large fluctuations between low water levels in spring and high levels in late summer and fall, the number of species and their cover per site were lower than along the free-flowing rivers. Regulated but unimpounded reaches were most similar to free-flowing rivers, having lower plant cover per site, but similar numbers of species. For reaches with reduced discharge, evidence was mixed; some variables were lower compared to free-flowing rivers whereas others were not. However, for the last two types of regulation, statistical power was low due to small sample sizes. Third, we classified all plant species according to their dispersal mechanisms and tested whether they respond differently to different types of regulated water-level regimes. Three out of four types of regulation had higher proportions of wind-dispersed species, and two out of four had lower proportions of species without specific mechanisms for dispersal, compared to free-flowing rivers, suggesting that dispersal ability is critical for persistence following regulation. Run-of-river impoundments had higher proportions of long-floating species and species with mechanisms for vegetative dispersal, suggesting that water dispersal may still be important despite fragmentation by dams. Fourth, plant species richness and cover varied with both local factors, such as water-level regime, and regional factors, such as length of the growing season. Presence of clay and silt in the river-margin soil, preregulation position of the contemporary river margin, non-reservoir sites, low altitudes, and long growing seasons were associated with high plant species richness and cover.
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