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991.
Identification of Kluyveromyces lactis Telomerase: Discontinuous Synthesis along the 30-Nucleotide-Long Templating Domain 总被引:2,自引:0,他引:2
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Telomeres in the budding yeast Kluyveromyces lactis consist of perfectly repeated 25-bp units, unlike the imprecise repeats at Saccharomyces cerevisiae telomeres and the short (6- to 8-bp) telomeric repeats found in many other eukaryotes. Telomeric DNA is synthesized by the ribonucleoprotein telomerase, which uses a portion of its RNA moiety as a template. K. lactis telomerase RNA, encoded by the TER1 gene, is ~1.3 kb long and contains a 30-nucleotide templating domain, the largest ever examined. To examine the mechanism of polymerization by this enzyme, we identified and analyzed telomerase activity from K. lactis whole-cell extracts. In this study, we exploited the length of the template and the precision of copying by K. lactis telomerase to examine primer elongation within one round of repeat synthesis. Under all in vitro conditions tested, K. lactis telomerase catalyzed only one round of repeat synthesis and remained bound to reaction products. We demonstrate that K. lactis telomerase polymerizes along the template in a discontinuous manner and stalls at two specific regions in the template. Increasing the amount of primer DNA-template RNA complementarity results in stalling, suggesting that the RNA-DNA hybrid is not unpaired during elongation in vitro and that lengthy duplexes hinder polymerization through particular regions of the template. We suggest that these observations provide an insight into the mechanism of telomerase and its regulation. 相似文献
992.
William I. Lutterschmidt Deborah I. Lutterschmidt Christopher R. Tracy Victor H. Hutchison 《Journal of thermal biology》1998,23(6):319-327
Intraperitoneal injections of either melatonin (MEL) or chlorpromazine (CPZ) significantly lowered preferred body temperature (Tb) of bullsnakes, Pituophis melanoleucus. Multiple comparison procedures showed that Tb for both MEL and CPZ treatments differed significantly from both the injected and non-injected control groups. However, Tb for MEL treatments did not differ from those of CPZ treatments (t=0.471; df=12; P=0.646), indicating that each drug has a similar effect on thermal selection. Our results obtained from time-course experiments support earlier experiments where a repeated measures design was used to test treatment effects of MEL and CPZ on thermal selection. However, we further show that injected controls (saline and ethanol injection) do not differ from non-injected controls (no injection) for both MEL and CPZ experiments. Although there are no differences between Tb of snakes receiving MEL or CPZ, time-course analyses indicate that the duration of thermoregulatory responses differ between MEL and CPZ treatments. This indicates that CPZ treatments may be more effective in increasing the amount of time required for individuals to return to normal preferred Tb or set temperature (Tset). The initial duration of thermoregulatory responses to the first injection of MEL differed significantly from the second injection. There were no differences in the duration of thermoregulatory responses between the first and second injections of CPZ. There are no data for the metabolic half-life of MEL in ectothermic vertebrates. Our study provides some information regarding the time-course of thermoregulatory responses to elevated levels of MEL via intraperitoneal injections of either MEL or CPZ, a metabolic antagonist of MEL. 相似文献
993.
The aim of this research was to investigate the nature of heterogeneity in
stomatal conductance and, in particular, to determine whether the
characteristic 'patchy' pattern of water infiltration is reflected in
measurements on individual stomata. Silicone rubber replicas were made of
primary leaves of glasshouse-grown Phaseolus vulgaris
L. plants, and the leaves were then infiltrated with water at controlled
sub-atmospheric gas pressures according to their estimated or measured
stomatal conductance. Seven leaves examined in detail all showed patchy
infiltration, and the mean sire of infiltrated areas was negatively
correlated with the prevailing stomatal conductance. In four of the leaves,
a one millimetre wide transect across the leaf was selected for further
detailed study. Measurements of mean peristomatal groove distance
(PGD) and stomatal frequency were made along the
transect and related to the state of infiltration. Analysis of variance
indicated that, in all four cases, variation in PGD
among patches was highly significant, but there was no significant
difference between patches of different infiltration categories. Thus,
local (patch-level) variation in stomatal aperture appeared to bear no
relation to the infiltration status of the patches. The dominant source of
stomatal variability was between individual pores in the same locality,
which accounted for 82% or more of the total variability. Taking into
account variation in stomatal frequency, correlations between predicted
stomatal conductance and the extent of infiltration were significant in
only one out of the seven leaves studied. Possible reasons for these
results are discussed. It is suggested that the infiltration method
misrepresents the underlying state of the stomata as being either open or
closed, when there is little evidence for this from measurements of
stomatal dimensions. For these unstressed plants under relatively stable
conditions, it is concluded that the 'unit of variability' in stomatal
heterogeneity may rest at the individual pore ('micro') scale, rather than
at the areolar patch ('macro') scale, or
above. 相似文献
994.
Tracy L. Connell Hancock Andria M. Costello Mary E. Lidstrom Ronald S. Oremland 《Applied and environmental microbiology》1998,64(8):2899-2905
A facultatively methylotrophic bacterium, strain IMB-1, that has been isolated from agricultural soil grows on methyl bromide (MeBr), methyl iodide, methyl chloride, and methylated amines, as well as on glucose, pyruvate, or acetate. Phylogenetic analysis of its 16S rRNA gene sequence indicates that strain IMB-1 classes in the alpha subgroup of the class Proteobacteria and is closely related to members of the genus Rhizobium. The ability of strain IMB-1 to oxidize MeBr to CO2 is constitutive in cells regardless of the growth substrate. Addition of cell suspensions of strain IMB-1 to soils greatly accelerates the oxidation of MeBr, as does pretreatment of soils with low concentrations of methyl iodide. These results suggest that soil treatment strategies can be devised whereby bacteria can effectively consume MeBr during field fumigations, which would diminish or eliminate the outward flux of MeBr to the atmosphere.Methyl bromide (MeBr) is a fumigant used in the cultivation of selected fruits, vegetables, and flowers and in the preservation of stored grains and structures. Use of MeBr as a pesticide increases the yield and quality of crops without leaving behind toxic residues characteristic of more complex organopesticides. However, because bromine released from MeBr destroys stratospheric ozone (18, 22, 29, 33), its use will be eliminated in the United States and elsewhere under the auspices of the Clean Air Act and the Montreal Protocol unless effective mechanisms which prevent its escape to the atmosphere can be found (36). Currently, much uncertainty exists with regard to the tropospheric residence time (τ) of MeBr, a factor which is used to calculate its ozone degradation potential (2). Estimates of τ range from ∼1.7 years when only oxidation by tropospheric OH radicals is considered (22) to less than 1.2 years when oceanic sinks are factored in (20). The discovery that soil bacteria oxidize MeBr from the atmosphere, when quantified and combined with the two preceding sinks, lowers τ to ∼0.8 years (32). Chemical destruction of MeBr occurs by hydrolysis, exchange with other halides, and reaction with organic matter (8, 9, 12), but its destruction by microorganisms has been noted in soils and aquatic environments (3, 16, 17a, 19, 23, 27, 28, 32). In aerobic environments, MeBr is oxidized to CO2 and Br− (3, 16, 23, 27).Bacterial oxidation of MeBr in soils has been reported both at very low (∼5 to 15 parts per trillion) ambient atmospheric mixing ratios (17a) and at the very high concentrations employed for field fumigation (23). The relative contributions that chemical reactions and bacterial oxidation make to the destruction of MeBr during agricultural fumigation are not yet known, but their combined effect will constrain the emissions of MeBr from soils. Reported destruction of MeBr within the soil matrix, as evidenced by the accumulation of Br−, can be substantial and account for as much as 39 to 70% of the applied MeBr in some cases (39, 40). Physical manipulations (e.g., soil compaction and deeper injection of MeBr) have been proposed to increase the retention time of MeBr within the soil matrix, thereby allowing for its more extensive degradation and subsequent decrease in its outward flux to the atmosphere (13). In addition, use of thicker, impermeable covering tarps has been proposed to reduce losses (14, 37), as has the substitution of methyl iodide for MeBr (11, 25). However, enhancement of microbial degradation of MeBr while it is present in the soil matrix may also be a means to eliminate emissions. This could be achieved by exploiting the ability of certain soil bacteria that use MeBr as a carbon and energy source (23). Here, we report further details on the characteristics of such an isolate (23), which we designate strain IMB-1. We demonstrate how the properties of IMB-1 can be used to greatly accelerate the oxidation of MeBr in fumigated soils. Because agricultural field fumigation represents the largest source of anthropogenic emissions of MeBr to the atmosphere, it is at least possible in theory that the overall goal of eliminating most human-derived emission of MeBr could be achieved by in situ biodegradation of this substance. 相似文献
995.
996.
George J. Gamboa Tracy L. Wacker Julie A. Scope Thomas J. Cornell Janet Shellman-Reeve 《Ethology : formerly Zeitschrift fur Tierpsychologie》1990,85(4):335-343
We examined how queens of the primitively eusocial wasp, Polistes fuscatus, stimulate foraging by workers in 10 small, post-worker-emergence field colonies. We experimentally increased colony needs, including needs of the brood, by removing a colony's most active foragers (thereby decreasing the colony's foraging rate), and found that the queen significantly increased both her level of activity and rate of aggressive interactions. Most aggressive interactions were directed at dominant workers. Removal of a colony's least active foragers, however, produced no such effect. Our results, together with those of Reeve & Gamboa (1983, 1987), indicate that queens are sensitive to brood needs, and that they behaviorally regulate worker foraging to match brood needs by increasing their level of activity and rate of aggressive interactions. 相似文献
997.
E F Hounsell A M Lawson M S Stoll D P Kane G C Cashmore R A Carruthers J Feeney T Feizi 《European journal of biochemistry》1989,186(3):597-610
Structural studies using liquid secondary ion mass spectrometry, gas liquid chromatography/mass spectrometry and 500-MHz 1H NMR are described of the major penta- and hexasaccharides of a fraction of human foetal gastrointestinal mucins. Glycoproteins from a blood group H active meconium pool were studied after depletion of Ii antigenic activities by immunoaffinity chromatography and treatment with mild acid hydrolysis to reduce the chain heterogeneity. Oligosaccharides were released by mild alkali/borohydride degradation and purified by Bio-Gel P4 chromatography and HPLC. Eleven penta- and hexasaccharides have been fully characterised as a result of this study and one previous report [Hounsell et al. (1988) Biochem. J. 256, 397-401] and information obtained on additional oligosaccharides present in small amounts. These oligosaccharides show the following features: (table; see text) Sequences in these oligosaccharides not commonly found in mucins so far studied are chain-terminating GlcNAc alpha 1-4Gal, repeating-type-I (Gal beta 1-3GlcNAc) backbones, the backbone branch GlcNAc beta 1-6(GlcNAc beta 1-3)Gal and the backbone sequence GlcNAc beta 1-6Gal beta 1- in the absence of a substituent at C3 of galactose. 相似文献
998.
R. A. Hutson D. E. Thompson P. A. Lawson R. P. Schocken-Itturino E. C. Böttger M. D. Collins 《Antonie van Leeuwenhoek》1993,64(3-4):273-283
The phylogenetic interrelationships of members of theClostridium botulinum complex of species was investigated by direct sequencing of their 16S rRNA genes. Comparative analysis of the 16S rRNA sequences demonstrated the presence of four phylogenetically distinct lineages corresponding to: i) proteolyticC. botulinum types A, B, and F, andC. sporogenes, ii) saccharolytic types B, E and F, iii) types C and D andC. novyi type A, and iv) type G andC. subterminale. The phylogenetic groupings obtained from the 16S rRNA were in complete agreement with the four divisions recognised within the species complex on the basis of phenotypic criteria. 相似文献
999.
James U. Van Dyke Luke M. McPhan Katie Howard Tracy Hamilton Liticia Ross Robyn J. Watts 《Austral ecology》2023,48(8):1681-1699
Freshwater turtles are important consumers in Australian freshwater ecosystems. They serve as scavengers, nutrient regulators, and as food sources and Totems for Traditional Owners throughout Australia. Despite their importance, most Australian freshwater turtle species are declining. The impact of winter wetland drying on turtle populations remains unknown, and winter exposure of hibernating turtles may be an important additional source of mortality. We aimed to examine turtle responses to seasonal and episodic wetland drying in wetlands using acoustic telemetry and active trapping. Wetlands were chosen that spanned a range of hydrological connectivity to the adjacent Edward/Kolety-Wakool River. We found that tagged Emydura macquarii typically exit wetlands disconnected from the adjacent permanent river prior to winter, and overwinter in the river. Female E. macquarii rapidly re-entered ‘home’ wetlands (wetlands in which they were initially tagged) the following spring, whereas males tended to leave the study area, returning occasionally. Although we were not able to evaluate a winter drying event, one of the wetlands experienced partial summer drying. All three local turtle species (E. macquarii, Chelodina expansa, C. longicollis) exited the wetland long before winter drying would have become a potential threat. Our results suggest that turtles in this system may be protected from winter wetland drying because they move to the adjacent permanent river prior to winter. Spending the winter in the river channel reduces the risks of being trapped in a drying wetland as temperatures drop in winter. 相似文献
1000.
Graham Moore Shahal Abbo Wing Cheung Tracie Foote Mike Gale Robert Koebner Andrew Leitch Ilia Leitch Tracy Money Patrick Stancombe Masahiro Yano Richard Flavell 《Genomics》1993,15(3)
Unlike mammalian genomes, cereal (Gramineae) genomes exhibit little suppression of CpG dinucleotides. In cereal genomes, however, most of the numerous potential recognition sites for CpG methylation-sensitive restriction enzymes are methylated. Analysis of cereal genomic libraries and of regions flanking genes indicates that unmethylated NotI sites are useful landmarks for regions containing genes/single-copy sequences. Studies of a rye chromosome arm indicate that its pericentromeric region has a reduced density of unmethylated NotI (and MluI) sites and therefore of genes. Unmethylated MluI and NruI sites are distributed nonrandomly in the genomes of wheat, barley, and rice. Analysis of the genomic blocks defined by these sites in wheat and barley indicates that they are most likely to have arisen by amplification. These observations form the basis of a proposed model for the organization and evolution of the wheat, barley, and rice genomes. 相似文献