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1.
The effects of mispair and nonpair correction in hybrid DNA on base ratios (G + C content) and total amounts of DNA 总被引:1,自引:0,他引:1
Base ratios and total DNA amounts can vary substantially between and within
higher taxa and genera, and even within species. Gene conversion is one of
several mechanisms that could cause such changes. For base substitutions,
disparity in conversion direction is accompanied by an equivalent disparity
in base ratio at the heterozygous site. Disparity in the direction of gene
conversion at meiosis is common and can be extreme. For transitions (which
give purine [R]/pyrimidine [Y] mispairs) and for transversions giving
unlike R/R and Y/Y mispairs in hybrid DNA, this disparity could give slow
but systematic changes in G + C percentage. For transversions giving like
R/R and Y/Y mispairs, it could change AT/TA and CG/GC ratios. From the
extent of correction direction disparity, one can deduce properties of
repair enzymes, such as the ability (1) to excise preferentially the purine
from one mispair and the pyrimidine from the other for two different R/Y
mispairs from a single heterozygous site and (2) to excise one base
preferentially from unlike R/R or Y/Y mispairs. Frame-shifts usually show
strong disparity in conversion direction, with preferential cutting of the
nonlooped or the looped-out strand of the nonpair in heterozygous h-DNA.
The opposite directions of disparity for frame-shifts and their intragenic
suppressors as Ascobolus suggest that repair enzymes have a strong,
systematic bias as to which strand is cut. The conversion spectra of
mutations induced with different mutagens suggest that the nonlooped strand
is preferentially cut, so that base additions generally convert to mutant
and deletions generally convert to wild-type forms. Especially in
nonfunctional or noncoding DNA, this could cause a general increase in DNA
amounts. Conversion disparity, selection, mutation, and other processes
interact, affecting rates of change in base ratios and total DNA.
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The sulfation pattern of chondroitin sulfate from articular cartilage explants in response to mechanical loading 总被引:5,自引:0,他引:5
Chondrocytes within articular cartilage experience complete unloading between loading cycles thereby utilizing mechanical signals to regulate their own anabolic and catabolic activities. Structural alterations of proteoglycans (PGs) during aging and the development of osteoarthritis (OA) have been reported; whether these can be attributed to altered load or compression is largely unknown. We report here on experiments in which the effect of intermittent loading on the fine structure of newly synthesized chondroitin sulfate (CS) in bovine articular cartilage explants was examined. Tissues were subjected for 6 days to cyclic compressive pressure using a sinusoidal waveform of 0.1, 0.5 or 1.0 Hz frequency with a peak stress of 0.5 MPa for a period of 5, 10 or 20 s, followed by an unloading period lasting 10, 100 or 1000 s. During the final 18 h of the culture, cartilage explants were radiolabeled with 50 microCi/ml D-6-[3H]glucosamine, and newly synthesized as well as endogenous CS chains were isolated after proteinase solubilization of the tissue. CS chains were depolymerized with chondroitinase ABC and ACII, and the 3H-digestion products were quantified after fractionation by high-performance anion-exchange chromatography using a CarboPac PA1 column. Intermittently applied cyclic mechanical loading did not affect the proportion of 4- and 6-sulfated disaccharide repeats, but caused a significant decrease in the abundance of the 4,6-disulfated nonreducing terminal galNAc residues. In addition, loading induced elongation of CS chains. Taken together, these data provide evidence for the first time that long-term in vitro loading results in marked and reproducible changes in the fine structure of newly synthesized CS, and that accumulation of such chains may in turn modify the physicochemical and biological response of articular cartilage. Moreover, data presented here suggest that in vitro dynamic compression of cartilage tissue can induce some of the same alterations in CS sulfation that have previously been shown to occur during the development of degenerative joint diseases such as OA. 相似文献
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Roelfsema MR Steinmeyer R Staal M Hedrich R 《The Plant journal : for cell and molecular biology》2001,26(1):1-13
Guard cells are electrically isolated from other plant cells and therefore offer the unique possibility to conduct current- and voltage-clamp recordings on single cells in an intact plant. Guard cells in their natural environment were impaled with double-barreled electrodes and found to exhibit three physiological states. A minority of cells were classified as far-depolarized cells. These cells exhibited positive membrane potentials and were dominated by the activity of voltage-dependent anion channels. All other cells displayed both outward and inward rectifying K+-channel activity. These cells were either depolarized or hyperpolarized, with average membrane potentials of -41 mV (SD 16) and -112 mV (SD 19), respectively. Depolarized guard cells extrude K+ through outward rectifying channels, while K+ is taken up via inward rectifying channels in hyperpolarized cells. Upon a light/dark transition, guard cells that were hyperpolarized in the light switched to the depolarized state. The depolarization was accompanied by a 35 pA decrease in pump current and an increase in the conductance of inward rectifying channels. Both an increase in pump current and a decrease in the conductance of the inward rectifier were triggered by blue light, while red light was ineffective. From these studies we conclude that light modulates plasma membrane transport through large membrane potential changes, reversing the K+-efflux via outward rectifying channels to a K+-influx via inward rectifying channels. 相似文献
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Marczak S Przezdziecka A Wicha J Steinmeyer A Zügel U 《Bioorganic & medicinal chemistry letters》2001,11(1):63-66
1Alpha,25-dihydroxyvitamin D3 diastereomer, differing from the parent compound in configuration at four asymmetric carbon atoms in the rings C/D and side chain (C13, C14, C17 and C20), was synthesized and shown to have a significant affinity for the vitamin D receptor. 相似文献
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ZK 156718, a low calcemic, antiproliferative, and prodifferentiating vitamin D analog. 总被引:1,自引:0,他引:1
Tanja Gaschott Andreas Steinmeyer Dieter Steinhilber Jürgen Stein 《Biochemical and biophysical research communications》2002,290(1):504-509
The physiologically active form of vitamin D, 1,25-dihydroxyvitamin D(3), plays an important role not only in the establishment and maintenance of calcium metabolism, but also in regulating cell growth and differentiation. Because the clinical usefulness of 1,25-dihydroxyvitamin D(3) is limited by its tendency to cause hypercalcemia, new analogs with a better therapeutic profile have been synthesized, including ZK 156718. We compared the effects of 1,25-dihydroxyvitamin D(3) and ZK 156718 on growth, differentiation, and on p21(Waf1/Cip1) and p27(Kip1) expression in human colon cancer cells (Caco-2). Whereas ZK 156718 at the concentration [10(-8) M] was as potent as 10(-6) M 1,25-dihydroxyvitamin D(3) in inducing differentiation and p21(Waf1/Cip1) expression, it was even more effective in inhibiting cell growth and stimulating p27(Kip1) expression than 1,25-dihydroxyvitamin D(3) itself. In summary, our study presents a new and potent vitamin D analog with a decreased metabolic stability, making it useful for the treatment of a diversity of clinical disorders. 相似文献
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M Matsuda A Tazumi S Kagawa T Sekizuka O Murayama JE Moore BC Millar 《BMC veterinary research》2006,2(1):1-4