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91.
A nearly universal feature of intron sequences is that even closely related
species exhibit a large number of insertion/deletion differences. The goal
of the analysis described here is to test whether the observed pattern of
insertion/deletion events in the genealogy of the myosin alkali light chain
(Mlc1) gene is consistent with neutrality, and if not, to determine the
underlying forces of evolutionary change. Mlc1 pre-mRNA is alternatively
spliced, and one constraint is that signals necessary for
tissue-specificity of directed splicing must be conserved. If the total
length of an intron is functionally constrained, then the distribution of
indels on branches of the gene genealogy should reflect a departure from
randomness. Here we perform a phylogenetic analysis, inferring ancestral
states wherever possible on a phylogeny of 29 alleles of Mlc1 from six
species of Drosophila. Observed patterns of indels on the genealogy were
compared to those from simulated data, with the result that we cannot
reject the null hypothesis of neutrality. A clear departure from a neutral
prediction was seen in the excess folding free energy predicted for the
introns flanking the alternatively spliced exon. Relative rate tests also
suggest a retardation in the rate of Mlc1 sequence evolution in the
simulans clade.
相似文献
92.
Norris V Alexandre S Bouligand Y Cellier D Demarty M Grehan G Gouesbet G Guespin J Insinna E Le Sceller L Maheu B Monnier C Grant N Onoda T Orange N Oshima A Picton L Polaert H Ripoll C Thellier M Valleton JM Verdus MC Vincent JC White G Wiggins P 《Biochimie》1999,81(8-9):915-920
A myriad different constituents or elements (genes, proteins, lipids, ions, small molecules etc.) participate in numerous physico-chemical processes to create bacteria that can adapt to their environments to survive, grow and, via the cell cycle, reproduce. We explore the possibility that it is too difficult to explain cell cycle progression in terms of these elements and that an intermediate level of explanation is needed. This level is that of hyperstructures. A hyperstructure is large, has usually one particular function, and contains many elements. Non-equilibrium, or even dissipative, hyperstructures that, for example, assemble to transport and metabolize nutrients may comprise membrane domains of transporters plus cytoplasmic metabolons plus the genes that encode the hyperstructure's enzymes. The processes involved in the putative formation of hyperstructures include: metabolite-induced changes to protein affinities that result in metabolon formation, lipid-organizing forces that result in lateral and transverse asymmetries, post-translational modifications, equilibration of water structures that may alter distributions of other molecules, transertion, ion currents, emission of electromagnetic radiation and long range mechanical vibrations. Equilibrium hyperstructures may also exist such as topological arrays of DNA in the form of cholesteric liquid crystals. We present here the beginning of a picture of the bacterial cell in which hyperstructures form to maximize efficiency and in which the properties of hyperstructures drive the cell cycle. 相似文献
93.
A likelihood approach for comparing synonymous and nonsynonymous nucleotide substitution rates, with application to the chloroplast genome 总被引:29,自引:24,他引:5
A model of DNA sequence evolution applicable to coding regions is
presented. This represents the first evolutionary model that accounts for
dependencies among nucleotides within a codon. The model uses the codon, as
opposed to the nucleotide, as the unit of evolution, and is parameterized
in terms of synonymous and nonsynonymous nucleotide substitution rates. One
of the model's advantages over those used in methods for estimating
synonymous and nonsynonymous substitution rates is that it completely
corrects for multiple hits at a codon, rather than taking a parsimony
approach and considering only pathways of minimum change between homologous
codons. Likelihood-ratio versions of the relative-rate test are constructed
and applied to data from the complete chloroplast DNA sequences of Oryza
sativa, Nicotiana tabacum, and Marchantia polymorpha. Results of these
tests confirm previous findings that substitution rates in the chloroplast
genome are subject to both lineage-specific and locus-specific effects.
Additionally, the new tests suggest tha the rate heterogeneity is due
primarily to differences in nonsynonymous substitution rates. Simulations
help confirm previous suggestions that silent sites are saturated, leaving
no evidence of heterogeneity in synonymous substitution rates.
相似文献
94.
Synopsis Two methods have been employed for measuring acid phosphatase activity in normal and regenerating epithelium of the female hairless hamster. The first method entails histochemical preparation followed by television scanning microdensitometric measurements using a Quantimet 720D. The second method involves incubation of freeze-dried epidermis in a suitable substrate medium followed by measurement of the fluorescence of the released product by a spectrophotofluorometer. The results were compared against each other by performing best-fit polynomial regression line analysis to the data produced by both methods. A correlation coefficient of 0.99 was obtained when interpolated data from the two best-fit curves were compared with each other. This indicates that the histochemical technique and the subsequent measurement using television scanning microdensitometry is quantitative and can, therefore, be employed in quantitative histochemistry. 相似文献
95.
ALEKSANDRA I. JOHANSEN ALICE EXNEROVÁ KATEŘINA HOTOVÁ SVÁDOVÁ PAVEL ŠTYS GABRIELLA GAMBERALE‐STILLE BIRGITTA S. TULLBERG 《Ecological Entomology》2010,35(5):602-610
1. Protective coloration in insects may be aposematic or cryptic, and some species change defensive strategy between instars. In Sweden, the adult striated shieldbugs Graphosoma lineatum (Heteroptera: Pentatomidae) undergo a seasonal colour change from pale brown and black striation in the pre‐hibernating adults, to red and black striation in the same post‐hibernating individuals. To the human eye the pre‐hibernating adults appear cryptic against the withered late summer vegetation, whereas the red and black post‐hibernating adults appear aposematic. This suggests a possibility of a functional colour change. However, what is cryptic to the human eye is not necessarily cryptic to a potential predator. 2. Therefore we tested the effect of coloration in adult G. lineatum on their detectability for avian predators. Great tits (Parus major) were trained to eat sunflower seeds hidden inside the emptied exoskeletons of pale or red G. lineatum. Then the detection time for both colour forms was measured in a dry vegetation environment. 3. The birds required a longer time to find the pale form of G. lineatum than the red one. The pale form appears more cryptic on withered late summer vegetation than the red form, not only to the human eye but also to avian predators. The result supports the idea that the adult individuals of G. lineatum undergo a functional change from a cryptic protective coloration to an aposematic one. 相似文献
96.
Georgeta Mocanu Doina Mihai Misu Moscovici Luc Picton Didier LeCerf 《International journal of biological macromolecules》2009,44(3):215-221
Microparticles of curdlan, synthesized through crosslinking with epichlorohydrin in organic suspension media, were chemically modified with the aim of introducing strongly and/or weakly acidic anionic and palmitoyl hydrophobic groups. Microparticles of both curdlan and curdlan derivatives were physico-chemically characterized. Study of the interaction with enzymes, such as lysozyme, and vaccines, such as tetanus anatoxin, showed a co-operative protein retention effect, induced by electrostatic and hydrophobic forces. The results of the in vitro release studies on support–protein complexes recommend them as potential controlled release systems. 相似文献
97.
T.A. Fenoradosoa C. Delattre C. Laroche A. Wadouachi V. Dulong L. Picton P. Andriamadio P. Michaud 《International journal of biological macromolecules》2009,45(2):140-145
Halymenia durvillei is a red seaweed with a great potential as sulphated galactan producer collected in the coastal waters of small island of Madagascar (Nosy-be in Indian Ocean). To elucidate the structure of its polysaccharide, NMR (1H and 13C), FTIR, HPAEC and different colorimetric methods were carried out. It has been shown that this polysaccharide, consisted mainly of galactose, was branched by xylose and galactose in minor amounts. Arabinose and fucose were also detected. This galactan was found highly sulphated (42%, w/w) and pyruvylated (1.8%, w/w). Analysis of glycosidic linkages by CPG-MS and 13C NMR indicated that the polysaccharide has the defining linear backbone of alternating 3-β-d-galactopyranosyl units and 4-linked α-l/d-galactopyranosyl residues. 3,6-Anhydrogalactose units have been also detected in minor quantity. This λ-carrageenan like polysaccharide has shown original sulphatation patterns with 2-O (26%) or 2/6-O (58%) sulphated 3-linked β-d-galactopyranosyl units and 6-O (19%) or 2/6-O (47%) 4-linked α-l/d-galactopyranosyl residues. 相似文献
98.
Spaak J Merlocco AC Soleas GJ Tomlinson G Morris BL Picton P Notarius CF Chan CT Floras JS 《American journal of physiology. Heart and circulatory physiology》2008,294(2):H605-H612
The cardiovascular benefits of light to moderate red wine consumption often have been attributed to its polyphenol constituents. However, the acute dose-related hemodynamic, vasodilator, and sympathetic neural effects of ethanol and red wine have not been characterized and compared in the same individual. We sought to test the hypotheses that responses to one and two alcoholic drinks differ and that red wine with high polyphenol content elicits a greater effect than ethanol alone. Thirteen volunteers (24-47 yr; 7 men, 6 women) drank wine, ethanol, and water in a randomized, single-blind trial on three occasions 2 wk apart. One drink of wine and ethanol increased blood alcohol to 38 +/- 2 and 39 +/- 2 mg/dl, respectively, and two drinks to 72 +/- 4 and 83 +/- 3 mg/dl, respectively. Wine quadrupled plasma resveratrol (P < 0.001) and increased catechin (P < 0.03). No intervention affected blood pressure. One drink had no heart rate effect, but two drinks of wine increased heart rate by 5.7 +/- 1.6 beats/min; P < 0.001). Cardiac output fell 0.8 +/- 0.3 l/min after one drink of ethanol and wine (both P < 0.02) but increased after two drinks of ethanol (+0.8 +/- 0.3 l/min) and wine (+1.2 +/- 0.3 l/min) (P < 0.01). One alcoholic drink did not alter muscle sympathetic nerve activity (MSNA), while two drinks increased MSNA by 9-10 bursts/min (P < 0.001). Brachial artery diameter increased after both one and two alcoholic drinks (P < 0.001). No beverage augmented, and the second wine dose attenuated (P = 0.02), flow-mediated vasodilation. One drink of ethanol dilates the brachial artery without activating sympathetic outflow, whereas two drinks increase MSNA, heart rate, and cardiac output. These acute effects, which exhibit a narrow dose response, are not modified by red wine polyphenols. 相似文献
99.
Eiser C Vance YH Glaser A Galvin H Horne B Picton S Stoner A Butler G 《Hormone research》2005,63(6):300-304
Background: We report the health-related quality of life (QOL) of survivors of childhood cancer (acute lymphoblastic leukaemia, ALL, or central nervous system, CNS, tumour), and whether or not they had growth hormone deficiency (GHD) requiring growth hormone treatment (GHT). Method: We assessed 77 survivors of childhood ALL (n = 51) or CNS tumours (n = 26), aged between 8-18 years, and free from disease for > or = 4 years. Survivors and their mothers independently rated survivors' QOL, and mothers completed semi-structured interviews to determine their views of the benefits and disadvantages of GHT. Results: Survivors, especially those treated for a CNS tumour, reported poorer QOL compared with UK population norms. Although survivors of ALL reported better QOL than survivors of CNS tumours, there were no differences depending on whether or not they were prescribed GHT. However, mothers reported that those prescribed GHT had worse QOL than those not. All but 2 survivors were responsible for their own injections. A minority of mothers were disappointed with the child's rate of growth, and reported that children experienced pain with injections. Conclusion: We conclude that QOL in survivors of childhood cancer is compromised compared with the normal population, especially following CNS tumours. Longitudinal studies are vital to determine whether GHT can contribute to improved QOL for cancer survivors, especially those who experience more intensive initial therapy regimes. 相似文献