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101.
Multiple duplications of yeast hexose transport genes in response to selection in a glucose-limited environment 总被引:11,自引:2,他引:9
When microbes evolve in a continuous, nutrient-limited environment, natural
selection can be predicted to favor genetic changes that give cells greater
access to limiting substrate. We analyzed a population of baker's yeast
that underwent 450 generations of glucose-limited growth. Relative to the
strain used as the inoculum, the predominant cell type at the end of this
experiment sustains growth at significantly lower steady-state glucose
concentrations and demonstrates markedly enhanced cell yield per mole
glucose, significantly enhanced high-affinity glucose transport, and
greater relative fitness in pairwise competition. These changes are
correlated with increased levels of mRNA hybridizing to probe generated
from the hexose transport locus HXT6. Further analysis of the evolved
strain reveals the existence of multiple tandem duplications involving two
highly similar, high- affinity hexose transport loci, HXT6 and HXT7.
Selection appears to have favored changes that result in the formation of
more than three chimeric genes derived from the upstream promoter of the
HXT7 gene and the coding sequence of HXT6. We propose a genetic mechanism
to account for these changes and speculate as to their adaptive
significance in the context of gene duplication as a common response of
microorganisms to nutrient limitation.
相似文献
102.
Vladimir S. Bondar Marelle G. Boersma Eugene L. Golovlev Jacques Vervoort Willem J.H. Van Berkel Zoya I. Finkelstein Inna P. Solyanikova Ludmila A. Golovleva Ivonne M.C.M. Rietjens 《Biodegradation》1998,9(6):475-486
Of all NMR observable isotopes 19F is the one perhaps most convenient for studies on biodegradation of environmental pollutants. The reasons underlying this potential of 19F NMR are discussed and illustrated on the basis of a study on the biodegradation of fluorophenols by four Rhodococcus strains. The results indicate marked differences between the biodegradation pathways of fluorophenols among the various Rhodococcus species. This holds not only for the level and nature of the fluorinated biodegradation pathway intermediates that accumulate, but also for the regioselectivity of the initial hydroxylation step. Several of the Rhodococcus species contain a phenol hydroxylase that catalyses the oxidative defluorination of ortho-fluorinated di- and trifluorophenols. Furthermore, it is illustrated how the 19F NMR technique can be used as a tool in the process of identification of an accumulated unknown metabolite, in this case most likely 5-fluoromaleylacetate. Altogether, the 19F NMR technique proved valid to obtain detailed information on the microbial biodegradation pathways of fluorinated organics, but also to provide information on the specificity of enzymes generally considered unstable and, for this reason, not much studied so far. 相似文献
103.
Acceptor specificity of the human leukocyte alpha3 fucosyltransferase: role of FucT-VII in the generation of selectin ligands 总被引:2,自引:2,他引:0
Britten CJ; van den Eijnden DH; McDowell W; Kelly VA; Witham SJ; Edbrooke MR; Bird MI; de Vries T; Smithers N 《Glycobiology》1998,8(4):321-327
The alpha3 fucosyltransferase, FucT-VII, is one of the key
glycosyltransferases involved in the biosynthesis of the sialyl Lewis X
(sLex) antigen on human leukocytes. The sialyl Lewis X antigen
(NeuAcalpha(2-3)Galbeta(1-4)[Fucalpha(1-3)]GlcNAc-R) is an essential
component of the recruitment of leukocytes to sites of inflammation,
mediating the primary interaction between circulating leukocytes and
activated endothelium. In order to characterize the enzymatic properties of
the leukocyte alpha3 fucosyltransferase FucT-VII, the enzyme has been
expressed in Trichoplusia ni insect cells. The enzyme is capable of
synthesizing both sLexand sialyl-dimeric-Lexstructures in vitro , from
3'-sialyl-lacNAc and VIM-2 structures, respectively, with only low levels
of fucose transfer observed to neutral or 3'-sulfated acceptors. Studies
using fucosylated NeuAcalpha(2-3)-(Galbeta(1- 4)GlcNAc)3-Me acceptors
demonstrate that FucT-VII is able to synthesize both di-fucosylated and
tri-fucosylated structures from mono- fucosylated precursors, but
preferentially fucosylates the distal GlcNAc within a polylactosamine
chain. Furthermore, the rate of fucosylation of the internal GlcNAc
residues is reduced once fucose has been added to the distal GlcNAc. These
results indicate that FucT-VII is capable of generating complex selectin
ligands, in vitro , however the order of fucose addition to the lactosamine
chain affects the rate of selectin ligand synthesis.
相似文献
104.
Biomass allocation in 6-month-old ectomycorrhizal Douglas fir seedlings was compared to that in nonmycorrhizal seedlings of
the same age, nutrient status and total biomass. Seedlings colonized by Rhizopogon vinicolor had the same distribution of biomass between roots, stems and needles, but only 56% of the total length of roots (including
mycorrhizal branches) compared to nonmycorrhizal seedlings. Laccaria laccata had no effect on distribution of biomass or root length of seedlings. The results for Rhizopogon provide direct evidence that the process of ectomycorrhizal colonization can significantly affect plant biomass allocation
by one or more mechanisms not directly related to altered nutrition or overall plant size. 相似文献
105.
BA Payseur HA Covert CJ Vinyard M Dagosto 《American journal of physical anthropology》1999,110(1):115-116
Payseur BA, Covert HA, Vinyard CJ, Dagosto M. 1999. New Body Mass Estimates for Omomys carteri, a Middle Eocene Primate From North America. Am J Phys Anthropol 109:41–52. This article included an incomplete Table 2. The final two columns, showing “Intercept” and “SEE” data were omitted. The complete Table 2, with these two columns included, is provided below. 相似文献
106.
J.-L. Primus Marelle G. Boersma Dominique Mandon Sjef Boeren Cees Veeger R. Weiss Ivonne M. C. M. Rietjens 《Journal of biological inorganic chemistry》1999,4(3):274-283
This study describes the catalytic properties of manganese microperoxidase 8 [Mn(III)MP8] compared to iron microperoxidase
8 [Fe(III)MP8]. The mini-enzymes were tested for pH-dependent activity and operational stability in peroxidase-type conversions,
using 2-methoxyphenol and 3,3′-dimethoxybenzidine, and in a cytochrome P450-like oxygen transfer reaction converting aniline
to para-aminophenol. For the peroxidase type of conversions the Fe to Mn replacement resulted in a less than 10-fold decrease in
the activity at optimal pH, whereas the aniline para-hydroxylation is reduced at least 30-fold. In addition it was observed that the peroxidase type of conversions are all fully
blocked by ascorbate and that aniline para-hydroxylation by Fe(III)MP8 is increased by ascorbate whereas aniline para-hydroxylation by Mn(III)MP8 is inhibited by ascorbate. Altogether these results indicate that different types of reactive
metal oxygen intermediates are involved in the various conversions. Compound I/II, scavenged by ascorbate, may be the reactive
species responsible for the peroxidase reactions, the polymerization of aniline and (part of) the oxygen transfer to aniline
in the absence of ascorbate. The para-hydroxylation of aniline by Fe(III)MP8, in the presence of ascorbate, must be mediated by another reactive iron-oxo species
which could be the electrophilic metal(III) hydroperoxide anion of microperoxidase 8 [M(III)OOH MP8]. The lower oxidative
potential of Mn, compared to Fe, may affect the reactivity of both compound I/II and the metal(III) hydroperoxide anion intermediate,
explaining the differential effect of the Fe to Mn substitution on the pH-dependent behavior, the rate of catalysis and the
operational stability of MP8.
Received: 29 September 1998 / Accepted: 16 February 1999 相似文献
107.
Extraction of pigments and fatty acids from the green alga Scenedesmus obliquus (Chlorophyceae) 总被引:1,自引:0,他引:1
In this paper, the efficiency of pigment and fatty acid extraction from resistant algae using Scenedesmus obliquus as an example was examined. We found that adding quartz sand and solvent to freeze-dried algal material and subsequent extraction in an ultrasound bath for 90min at –4°C resulted in excellent extraction of these compounds. This extraction method was compared with a method regularly used for extraction of fatty acids and pigments, i.e. addition of solvents to algal material with subsequent incubation. Our extraction using the ultrasound and sand method was about twice as efficient as this method for both pigments and fatty acids. The ultrasound method is simple, extracts over 90% of the different substances in one step and conserves the relationships of pigments and fatty acids. In addition, no alteration- or breakdown products were observed with the new method. Thus, this method allows accurate quantitative extraction of both pigments and fatty acids from Scenedesmus obliquus and other algae. The method was also been found to be as effective for Cryptomonas erosa (Cryptophyceae), Cyclotella meneghiniana (Bacillariophyceae), Microcystis aeruginosa (Cyanophyceae), and Staurastrum paradoxum (Chlorophyceae, Desmidiaceae) and is thus applicable to a wide spectrum of algae. 相似文献
108.
Antiestrogens specifically up-regulate bone morphogenetic protein-4 promoter activity in human osteoblastic cells 总被引:6,自引:0,他引:6
van den Wijngaard A Mulder WR Dijkema R Boersma CJ Mosselman S van Zoelen EJ Olijve W 《Molecular endocrinology (Baltimore, Md.)》2000,14(5):623-633
Bone morphogenetic protein-4 (BMP-4) plays an important role in the onset of endochondral bone formation in humans, and a reduction in BMP-4 expression has been associated with a variety of bone diseases. Here we describe, by transient transfection assays in bone cells, that the human BMP-4 promoter recently characterized in our laboratory can be stimulated specifically by antiestrogens but not by estrogens or other steroid hormones. This activity is dependent on the presence of the estrogen receptor (ER)-alpha, although the promoter lacks a consensus estrogen-responsive element. No activity was observed in the presence of ERbeta, but synergy was observed when both ER subtypes were cotransfected. The observed stimulation of BMP-4 promoter activity by antiestrogens appeared bone cell specific and was reversed upon addition of estrogens. Since antiestrogens are known to be effective in hormone replacement therapies for postmenopausal women, this observation may help to develop new strategies for treatment and prevention of osteoporosis. 相似文献
109.
Zhang C Reiter C Eiserich JP Boersma B Parks DA Beckman JS Barnes S Kirk M Baldus S Darley-Usmar VM White CR 《The Journal of biological chemistry》2001,276(29):27159-27165
The myeloperoxidase-derived oxidant hypochlorous acid (HOCl) is thought to contribute to endothelial dysfunction, but the mechanisms underlying this inhibitory effect are unknown. The present study tested the hypothesis that HOCl and L-arginine (L-Arg) react to form novel compounds that adversely affect endothelial function by inhibiting nitric oxide (NO) formation. Using spectrophotometric techniques, we found that HOCl and L-Arg react rapidly (k = 7.1 x 10(5) m(-1) s(-1)) to form two major products that were identified by mass spectrometry as monochlorinated and dichlorinated adducts of L-Arg. Pretreatment of bovine aortic endothelial cells with the chlorinated L-Arg metabolites (Cl-l-Arg) inhibited the -induced formation of the NO metabolites nitrate (NO(3)(-)) and nitrite (NO(2)(-)) in a concentration-dependent manner. Preincubation of rat aortic ring segments with Cl-L-Arg resulted in concentration-dependent inhibition of acetylcholine-induced relaxation. In contrast, blood vessels relaxed normally to the endothelium-independent vasodilator sodium nitroprusside. In vivo administration of Cl-L-Arg to anesthetized rats increased carotid artery vascular resistance. A greater than 10-fold excess of L-Arg was required to reverse the inhibitory effects of Cl-L-Arg in vivo and in vitro. Reaction of HOCl with D-arginine (D-Arg) did not result in the formation of inhibitory products. These results suggest that HOCl reacts with L-Arg to form chlorinated products that act as nitric-oxide synthase inhibitors. 相似文献
110.
Predator-induced life-history changes and the coexistence of five taxa in a Daphnia species complex 总被引:1,自引:0,他引:1
Interspecific hybridization is common in water fleas of the Daphnia galeata species complex (e.g. D. galeata , D. cucullata , D. hyalina and their interspecific hybrids). We studied the effect of fish on the life histories of five taxa of this species complex originating from the Plußsee, northern Germany. Using four clones per taxon, we found that fish kairomones reduce size at birth and size at maturity significantly. For size at maturity larger taxa showed a significantly stronger reaction to fish kairomones than the smaller taxa. With respect to the intrinsic rate of increase, r , we compared two predation regimes (positive size selective and not selective). We found that under the fish predation regime most clones had a higher r when cultured with fish kairomones, leading to a higher r , and a stronger reaction for the smaller taxa. We conclude that fish predation might be an important factor influencing the co-occurrence of Daphnia parental taxa with their hybrids. 相似文献