排序方式: 共有28条查询结果,搜索用时 15 毫秒
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BACKGROUND: The macrolide antibiotic tylosin is composed of a polyketide lactone substituted with three deoxyhexose sugars. In order to produce tylosin efficiently, Streptomyces fradiae presumably requires control mechanisms that balance the yields of the constituent metabolic pathways together with switches that allow for temporal regulation of antibiotic production. In addition to possible metabolic feedback and/or other signalling devices, such control probably involves interplay between specific regulatory proteins. Prior to the present work, however, no candidate regulatory gene(s) had been identified in S. fradiae. RESULTS: DNA sequencing has shown that the tylosin biosynthetic gene cluster, within which four open reading frames utilise the rare TTA codon, contains at least five candidate regulatory genes, one of which (tylP) encodes a gamma-butyrolactone signal receptor for which tylQ is a probable target. Two other genes (tylS and tylT) encode pathway-specific regulatory proteins of the Streptomyces antibiotic regulatory protein (SARP) family and a fifth, tylR, has been shown by mutational analysis to control various aspects of tylosin production. CONCLUSIONS: The tyl genes of S. fradiae include the richest collection of regulators yet encountered in a single antibiotic biosynthetic gene cluster. Control of tylosin biosynthesis is now amenable to detailed study, and manipulation of these various regulatory genes is likely to influence yields in tylosin-production fermentations. 相似文献
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Claire Wilson J. Stephen Clark Andrea L. Bate Alexander J. Blake Trevor Grinter Simon J. Teat 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(11):1326-1329
The novel bicyclic and tricyclic systems dimethyl (4aS*,6S*)-6-methoxy-7-oxo-4a,5,6,7,8,9-hexahydro-2H-benzocycloheptene-3,4-dicarboxylate, C16H20O6, (I), dimethyl (4aS*,6R*)-6-methoxy-7-oxo-4a,5,6,7,8,9-hexahydro-2H-benzocycloheptene-3,4-dicarboxylate, C16H20O6, (II), (3aS*,9R*,10aS*,10bR*)-9-methoxy-2-oxa-1,3a,4,6,7,8,9,10,10a,10b-decahydro-3H-cyclohepta[e]indene-1,3,8-trione, C14H16O5, (III), and (1S*,2R*,9S*,10aR*)-9-methoxy-8-oxo-1,2,3,5,6,7,8,9,10,10a-decahydrobenzocyclooctene-1,2-dicarboxylic acid, C15H20O6, (IV), have been crystallographically characterized, allowing the determination of the relative configuration of the stereogenic centres. The poor quality of the dicarboxylic acid crystals necessitated the use of synchrotron radiation. 相似文献
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L. C. Bate S. E. Lindberg A. W. Andren 《Journal of Radioanalytical and Nuclear Chemistry》1976,32(1):125-135
Instrumental neutron activation analysis was used to determine the elemental concentrations in water and air solid samples
collected on Nuclepore and Whatman filters from the Walker Branch Watershed. The results from this study show that the trace
element concentrations removed by water from the watershed vary seasonally, as well as geographically. The data point up the
usefulness and versatility of absolute neutron activation analysis. The NBS Standard Orchard Leaves was assayed in a similar
manner, and good agreement was obtained between results here and standard values. 相似文献
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Joanne Dumville David J. Bate John A. Leake Eric R. Wallach 《Mikrochimica acta》1995,120(1-4):101-110
In laser microprobe mass spectrometry (LAMMS), the ablated ions are normally extracted using a 3-kV potential difference. This constant extraction bias continuously extracts ions as they are formed in the plasma and reduces the chance of any thermal equilibration. In contrast, in pulsed extraction a delay between ion formation and extraction should allow for partial thermal equilibration. This would reduce the energy spread of the ions entering the spectrometer and would allow more of the ablated ions to be detected, both effects giving a spectrum more representative of the original sample composition. In this paper, the energy distributions of ions from single element samples are shown experimentally to be reduced at defined delays. This arises from some extent of thermal equilibration (as predicted) and also bunching of the ions at the detector due to the transient extraction profile which causes velocity compaction. An additional result is that heavier elements require longer delays before extraction for the ions to equilibrate, because of their larger initial energy spreads. This mass-dependence of the time to reach equilibrium limits improvement in quantification of LAMMS by pulsed extraction without further modification. A LAMMS instrument designed to extract the ions initially at a low potential (to allow for equilibration) and then to apply a pulsed voltage to each bunch of ions of different mass would improve quantification. 相似文献
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N. G. Bate 《The Journal of the Operational Research Society》1994,45(8):927-933
When multiple work-patterns (also called calendars) are present in a network, it is quite common that there is no critical path spanning the network. This paper explains why this is so. To address the problem, the normal definition of criticality in project networks is split into two-delay criticality, and compress criticality. 相似文献
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Michael Bate 《Transformation Groups》2009,14(1):29-40
Let G be a reductive group acting on an affine variety X, let x ∈ X be a point whose G-orbit is not closed, and let S be a G-stable closed subvariety of X which meets the closure of the G-orbit of x but does not contain x. In this paper we study G. R. Kempf’s optimal class Ω
G
(x; S) of cocharacters of G attached to the point x; in particular, we consider how this optimality transfers to subgroups of G.
Suppose K is a G-completely reducible subgroup of G which fixes x, and let H = C
G
(K)0. Our main result says that the H-orbit of x is also not closed, and the optimal class Ω
H
(x; S) for H simply consists of the cocharacters in Ω
G
(x; S) which evaluate in H. We apply this result in the case that G acts on its Lie algebra via the adjoint representation to obtain some new information about cocharacters associated with
nilpotent elements in good characteristic. 相似文献